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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v11 03/17] vpci: use per-domain PCI lock to protect vpci structure
On 12/21/23 09:05, Roger Pau Monné wrote:
> On Sat, Dec 02, 2023 at 01:27:03AM +0000, Volodymyr Babchuk wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>
>> Use a previously introduced per-domain read/write lock to check
>> whether vpci is present, so we are sure there are no accesses to the
>> contents of the vpci struct if not. This lock can be used (and in a
>> few cases is used right away) so that vpci removal can be performed
>> while holding the lock in write mode. Previously such removal could
>> race with vpci_read for example.
>>
>> When taking both d->pci_lock and pdev->vpci->lock, they should be
>> taken in this exact order: d->pci_lock then pdev->vpci->lock to avoid
>> possible deadlock situations.
>>
>> 1. Per-domain's pci_rwlock is used to protect pdev->vpci structure
>> from being removed.
>>
>> 2. Writing the command register and ROM BAR register may trigger
>> modify_bars to run, which in turn may access multiple pdevs while
>> checking for the existing BAR's overlap. The overlapping check, if
>> done under the read lock, requires vpci->lock to be acquired on both
>> devices being compared, which may produce a deadlock. It is not
>> possible to upgrade read lock to write lock in such a case. So, in
>> order to prevent the deadlock, use d->pci_lock instead. To prevent
>> deadlock while locking both hwdom->pci_lock and dom_xen->pci_lock,
>> always lock hwdom first.
>
> FWIW (I think it was also mentioned in the previous version) for
> devices assigned to dom_xen taking the hwdom lock should be enough.
> There are no other accesses to such devices that don't originate from
> hwdom, and it's not possible to degassing devices from dom_xen.
OK, we will re-word the commit message and make the change in vpci_{read,write}.
>
>>
>> All other code, which doesn't lead to pdev->vpci destruction and does
>> not access multiple pdevs at the same time, can still use a
>> combination of the read lock and pdev->vpci->lock.
>>
>> 3. Drop const qualifier where the new rwlock is used and this is
>> appropriate.
>>
>> 4. Do not call process_pending_softirqs with any locks held. For that
>> unlock prior the call and re-acquire the locks after. After
>> re-acquiring the lock there is no need to check if pdev->vpci exists:
>> - in apply_map because of the context it is called (no race condition
>> possible)
>> - for MSI/MSI-X debug code because it is called at the end of
>> pdev->vpci access and no further access to pdev->vpci is made
>>
>> 5. Use d->pci_lock around for_each_pdev and pci_get_pdev_by_domain
>> while accessing pdevs in vpci code.
>>
>> 6. We are removing multiple ASSERT(pcidevs_locked()) instances because
>> they are too strict now: they should be corrected to
>> ASSERT(pcidevs_locked() || rw_is_locked(&d->pci_lock)), but problem is
>> that mentioned instances does not have access to the domain
>> pointer and it is not feasible to pass a domain pointer to a function
>> just for debugging purposes.
>>
>> Suggested-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
>>
>> ---
>> Changes in v11:
>> - Fixed commit message regarding possible spinlocks
>> - Removed parameter from allocate_and_map_msi_pirq(), which was added
>> in the prev version. Now we are taking pcidevs_lock in
>> physdev_map_pirq()
>> - Returned ASSERT to pci_enable_msi
>> - Fixed case when we took read lock instead of write one
>> - Fixed label indentation
>>
>> Changes in v10:
>> - Moved printk pas locked area
>> - Returned back ASSERTs
>> - Added new parameter to allocate_and_map_msi_pirq() so it knows if
>> it should take the global pci lock
>> - Added comment about possible improvement in vpci_write
>> - Changed ASSERT(rw_is_locked()) to rw_is_write_locked() in
>> appropriate places
>> - Renamed release_domain_locks() to release_domain_write_locks()
>> - moved domain_done label in vpci_dump_msi() to correct place
>> Changes in v9:
>> - extended locked region to protect vpci_remove_device and
>> vpci_add_handlers() calls
>> - vpci_write() takes lock in the write mode to protect
>> potential call to modify_bars()
>> - renamed lock releasing function
>> - removed ASSERT()s from msi code
>> - added trylock in vpci_dump_msi
>>
>> Changes in v8:
>> - changed d->vpci_lock to d->pci_lock
>> - introducing d->pci_lock in a separate patch
>> - extended locked region in vpci_process_pending
>> - removed pcidevs_lockis vpci_dump_msi()
>> - removed some changes as they are not needed with
>> the new locking scheme
>> - added handling for hwdom && dom_xen case
>> ---
>> xen/arch/x86/hvm/vmsi.c | 22 +++++++--------
>> xen/arch/x86/hvm/vmx/vmx.c | 2 --
>> xen/arch/x86/irq.c | 8 +++---
>> xen/arch/x86/msi.c | 10 ++-----
>> xen/arch/x86/physdev.c | 2 ++
>> xen/drivers/passthrough/pci.c | 9 +++---
>> xen/drivers/vpci/header.c | 18 ++++++++++++
>> xen/drivers/vpci/msi.c | 28 +++++++++++++++++--
>> xen/drivers/vpci/msix.c | 52 ++++++++++++++++++++++++++++++-----
>> xen/drivers/vpci/vpci.c | 50 +++++++++++++++++++++++++++++++--
>> 10 files changed, 160 insertions(+), 41 deletions(-)
>>
>> diff --git a/xen/arch/x86/hvm/vmsi.c b/xen/arch/x86/hvm/vmsi.c
>> index 128f236362..03caf91bee 100644
>> --- a/xen/arch/x86/hvm/vmsi.c
>> +++ b/xen/arch/x86/hvm/vmsi.c
>> @@ -468,7 +468,7 @@ int msixtbl_pt_register(struct domain *d, struct pirq
>> *pirq, uint64_t gtable)
>> struct msixtbl_entry *entry, *new_entry;
>> int r = -EINVAL;
>>
>> - ASSERT(pcidevs_locked());
>> + ASSERT(pcidevs_locked() || rw_is_locked(&d->pci_lock));
>> ASSERT(rw_is_write_locked(&d->event_lock));
>>
>> if ( !msixtbl_initialised(d) )
>> @@ -538,7 +538,7 @@ void msixtbl_pt_unregister(struct domain *d, struct pirq
>> *pirq)
>> struct pci_dev *pdev;
>> struct msixtbl_entry *entry;
>>
>> - ASSERT(pcidevs_locked());
>> + ASSERT(pcidevs_locked() || rw_is_locked(&d->pci_lock));
>> ASSERT(rw_is_write_locked(&d->event_lock));
>>
>> if ( !msixtbl_initialised(d) )
>> @@ -684,7 +684,7 @@ static int vpci_msi_update(const struct pci_dev *pdev,
>> uint32_t data,
>> {
>> unsigned int i;
>>
>> - ASSERT(pcidevs_locked());
>> + ASSERT(rw_is_locked(&pdev->domain->pci_lock));
>>
>> if ( (address & MSI_ADDR_BASE_MASK) != MSI_ADDR_HEADER )
>> {
>> @@ -725,8 +725,8 @@ void vpci_msi_arch_update(struct vpci_msi *msi, const
>> struct pci_dev *pdev)
>> int rc;
>>
>> ASSERT(msi->arch.pirq != INVALID_PIRQ);
>> + ASSERT(rw_is_locked(&pdev->domain->pci_lock));
>>
>> - pcidevs_lock();
>> for ( i = 0; i < msi->vectors && msi->arch.bound; i++ )
>> {
>> struct xen_domctl_bind_pt_irq unbind = {
>> @@ -745,7 +745,6 @@ void vpci_msi_arch_update(struct vpci_msi *msi, const
>> struct pci_dev *pdev)
>>
>> msi->arch.bound = !vpci_msi_update(pdev, msi->data, msi->address,
>> msi->vectors, msi->arch.pirq,
>> msi->mask);
>> - pcidevs_unlock();
>> }
>>
>> static int vpci_msi_enable(const struct pci_dev *pdev, unsigned int nr,
>> @@ -778,15 +777,14 @@ int vpci_msi_arch_enable(struct vpci_msi *msi, const
>> struct pci_dev *pdev,
>> int rc;
>>
>> ASSERT(msi->arch.pirq == INVALID_PIRQ);
>> + ASSERT(rw_is_locked(&pdev->domain->pci_lock));
>> rc = vpci_msi_enable(pdev, vectors, 0);
>> if ( rc < 0 )
>> return rc;
>> msi->arch.pirq = rc;
>>
>> - pcidevs_lock();
>> msi->arch.bound = !vpci_msi_update(pdev, msi->data, msi->address,
>> vectors,
>> msi->arch.pirq, msi->mask);
>> - pcidevs_unlock();
>>
>> return 0;
>> }
>> @@ -797,8 +795,8 @@ static void vpci_msi_disable(const struct pci_dev *pdev,
>> int pirq,
>> unsigned int i;
>>
>> ASSERT(pirq != INVALID_PIRQ);
>> + ASSERT(rw_is_locked(&pdev->domain->pci_lock));
>>
>> - pcidevs_lock();
>> for ( i = 0; i < nr && bound; i++ )
>> {
>> struct xen_domctl_bind_pt_irq bind = {
>> @@ -814,7 +812,6 @@ static void vpci_msi_disable(const struct pci_dev *pdev,
>> int pirq,
>> write_lock(&pdev->domain->event_lock);
>> unmap_domain_pirq(pdev->domain, pirq);
>> write_unlock(&pdev->domain->event_lock);
>> - pcidevs_unlock();
>> }
>>
>> void vpci_msi_arch_disable(struct vpci_msi *msi, const struct pci_dev *pdev)
>> @@ -854,6 +851,7 @@ int vpci_msix_arch_enable_entry(struct vpci_msix_entry
>> *entry,
>> int rc;
>>
>> ASSERT(entry->arch.pirq == INVALID_PIRQ);
>> + ASSERT(rw_is_locked(&pdev->domain->pci_lock));
>> rc = vpci_msi_enable(pdev, vmsix_entry_nr(pdev->vpci->msix, entry),
>> table_base);
>> if ( rc < 0 )
>> @@ -861,7 +859,6 @@ int vpci_msix_arch_enable_entry(struct vpci_msix_entry
>> *entry,
>>
>> entry->arch.pirq = rc;
>>
>> - pcidevs_lock();
>> rc = vpci_msi_update(pdev, entry->data, entry->addr, 1,
>> entry->arch.pirq,
>> entry->masked);
>> if ( rc )
>> @@ -869,7 +866,6 @@ int vpci_msix_arch_enable_entry(struct vpci_msix_entry
>> *entry,
>> vpci_msi_disable(pdev, entry->arch.pirq, 1, false);
>> entry->arch.pirq = INVALID_PIRQ;
>> }
>> - pcidevs_unlock();
>>
>> return rc;
>> }
>> @@ -895,6 +891,8 @@ int vpci_msix_arch_print(const struct vpci_msix *msix)
>> {
>> unsigned int i;
>>
>> + ASSERT(rw_is_locked(&msix->pdev->domain->pci_lock));
>> +
>> for ( i = 0; i < msix->max_entries; i++ )
>> {
>> const struct vpci_msix_entry *entry = &msix->entries[i];
>> @@ -913,7 +911,9 @@ int vpci_msix_arch_print(const struct vpci_msix *msix)
>> struct pci_dev *pdev = msix->pdev;
>>
>> spin_unlock(&msix->pdev->vpci->lock);
>> + read_unlock(&pdev->domain->pci_lock);
>> process_pending_softirqs();
>> + read_lock(&pdev->domain->pci_lock);
>> /* NB: we assume that pdev cannot go away for an alive domain.
>> */
>> if ( !pdev->vpci || !spin_trylock(&pdev->vpci->lock) )
>> return -EBUSY;
>> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
>> index 5663bc0178..dd836e49f3 100644
>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>> @@ -413,8 +413,6 @@ static int cf_check vmx_pi_update_irte(const struct vcpu
>> *v,
>>
>> spin_unlock_irq(&desc->lock);
>>
>> - ASSERT(pcidevs_locked());
>
> Can't you do?
>
> ASSERT(pcidevs_locked() || rw_is_locked(&msi_desc->dev->domain->pci_lock));
>
> The iommu_update_ire_from_msi() call below does rely on msi_desc->dev
> being set, so we can do the same here.
Yes, we will reintroduce the modified ASSERT
>
>> -
>> return iommu_update_ire_from_msi(msi_desc, &msi_desc->msg);
>>
>> unlock_out:
>> diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
>> index 50e49e1a4b..4d89d9af99 100644
>> --- a/xen/arch/x86/irq.c
>> +++ b/xen/arch/x86/irq.c
>> @@ -2166,7 +2166,7 @@ int map_domain_pirq(
>> struct pci_dev *pdev;
>> unsigned int nr = 0;
>>
>> - ASSERT(pcidevs_locked());
>> + ASSERT(pcidevs_locked() || rw_is_locked(&d->pci_lock));
>>
>> ret = -ENODEV;
>> if ( !cpu_has_apic )
>> @@ -2323,7 +2323,7 @@ int unmap_domain_pirq(struct domain *d, int pirq)
>> if ( (pirq < 0) || (pirq >= d->nr_pirqs) )
>> return -EINVAL;
>>
>> - ASSERT(pcidevs_locked());
>> + ASSERT(pcidevs_locked() || rw_is_locked(&d->pci_lock));
>> ASSERT(rw_is_write_locked(&d->event_lock));
>>
>> info = pirq_info(d, pirq);
>> @@ -2888,6 +2888,8 @@ int allocate_and_map_msi_pirq(struct domain *d, int
>> index, int *pirq_p,
>> {
>> int irq, pirq, ret;
>>
>> + ASSERT(pcidevs_locked() || rw_is_locked(&d->pci_lock));
>> +
>> switch ( type )
>> {
>> case MAP_PIRQ_TYPE_MSI:
>> @@ -2917,7 +2919,6 @@ int allocate_and_map_msi_pirq(struct domain *d, int
>> index, int *pirq_p,
>>
>> msi->irq = irq;
>>
>> - pcidevs_lock();
>
> Since you remove the locking here, it might be good to replace with an
> assert.
The ASSERT was added at the beginning of this function - see above
>
>> /* Verify or get pirq. */
>> write_lock(&d->event_lock);
>> pirq = allocate_pirq(d, index, *pirq_p, irq, type, &msi->entry_nr);
>> @@ -2933,7 +2934,6 @@ int allocate_and_map_msi_pirq(struct domain *d, int
>> index, int *pirq_p,
>>
>> done:
>> write_unlock(&d->event_lock);
>> - pcidevs_unlock();
>> if ( ret )
>> {
>> switch ( type )
>> diff --git a/xen/arch/x86/msi.c b/xen/arch/x86/msi.c
>> index 335c0868a2..6a548611a5 100644
>> --- a/xen/arch/x86/msi.c
>> +++ b/xen/arch/x86/msi.c
>> @@ -602,7 +602,7 @@ static int msi_capability_init(struct pci_dev *dev,
>> unsigned int i, mpos;
>> uint16_t control;
>>
>> - ASSERT(pcidevs_locked());
>> + ASSERT(pcidevs_locked() || rw_is_locked(&dev->domain->pci_lock));
>> pos = pci_find_cap_offset(dev->sbdf, PCI_CAP_ID_MSI);
>> if ( !pos )
>> return -ENODEV;
>> @@ -771,7 +771,7 @@ static int msix_capability_init(struct pci_dev *dev,
>> if ( !pos )
>> return -ENODEV;
>>
>> - ASSERT(pcidevs_locked());
>> + ASSERT(pcidevs_locked() || rw_is_locked(&dev->domain->pci_lock));
>>
>> control = pci_conf_read16(dev->sbdf, msix_control_reg(pos));
>> /*
>> @@ -988,8 +988,6 @@ static int __pci_enable_msi(struct pci_dev *pdev, struct
>> msi_info *msi,
>> {
>> struct msi_desc *old_desc;
>>
>> - ASSERT(pcidevs_locked());
>> -
>> if ( !pdev )
>> return -ENODEV;
>>
>> @@ -1043,8 +1041,6 @@ static int __pci_enable_msix(struct pci_dev *pdev,
>> struct msi_info *msi,
>> {
>> struct msi_desc *old_desc;
>>
>> - ASSERT(pcidevs_locked());
>> -
>> if ( !pdev || !pdev->msix )
>> return -ENODEV;
>
> For both __pci_enable_msi{,x}(), can you move the check after making
> sure that pdev != NULL, and then expand the condition to cover
> pdev->domain->pci_lock taken?
Yes, will do
>
>>
>> @@ -1154,7 +1150,7 @@ int pci_prepare_msix(u16 seg, u8 bus, u8 devfn, bool
>> off)
>> int pci_enable_msi(struct pci_dev *pdev, struct msi_info *msi,
>> struct msi_desc **desc)
>> {
>> - ASSERT(pcidevs_locked());
>> + ASSERT(pcidevs_locked() || rw_is_locked(&pdev->domain->pci_lock));
>>
>> if ( !use_msi )
>> return -EPERM;
>> diff --git a/xen/arch/x86/physdev.c b/xen/arch/x86/physdev.c
>> index 47c4da0af7..369c9e788c 100644
>> --- a/xen/arch/x86/physdev.c
>> +++ b/xen/arch/x86/physdev.c
>> @@ -123,7 +123,9 @@ int physdev_map_pirq(domid_t domid, int type, int
>> *index, int *pirq_p,
>>
>> case MAP_PIRQ_TYPE_MSI:
>> case MAP_PIRQ_TYPE_MULTI_MSI:
>> + pcidevs_lock();
>> ret = allocate_and_map_msi_pirq(d, *index, pirq_p, type, msi);
>> + pcidevs_unlock();
>> break;
>>
>> default:
>> diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
>> index b8ad4fa07c..182da45acb 100644
>> --- a/xen/drivers/passthrough/pci.c
>> +++ b/xen/drivers/passthrough/pci.c
>> @@ -750,7 +750,6 @@ int pci_add_device(u16 seg, u8 bus, u8 devfn,
>> pdev->domain = hardware_domain;
>> write_lock(&hardware_domain->pci_lock);
>> list_add(&pdev->domain_list, &hardware_domain->pdev_list);
>> - write_unlock(&hardware_domain->pci_lock);
>>
>> /*
>> * For devices not discovered by Xen during boot, add vPCI handlers
>> @@ -759,18 +758,18 @@ int pci_add_device(u16 seg, u8 bus, u8 devfn,
>> ret = vpci_add_handlers(pdev);
>> if ( ret )
>> {
>> - printk(XENLOG_ERR "Setup of vPCI failed: %d\n", ret);
>> - write_lock(&hardware_domain->pci_lock);
>> list_del(&pdev->domain_list);
>> write_unlock(&hardware_domain->pci_lock);
>> pdev->domain = NULL;
>> + printk(XENLOG_ERR "Setup of vPCI failed: %d\n", ret);
>> goto out;
>> }
>> + write_unlock(&hardware_domain->pci_lock);
>> ret = iommu_add_device(pdev);
>> if ( ret )
>> {
>> - vpci_remove_device(pdev);
>> write_lock(&hardware_domain->pci_lock);
>> + vpci_remove_device(pdev);
>> list_del(&pdev->domain_list);
>> write_unlock(&hardware_domain->pci_lock);
>> pdev->domain = NULL;
>> @@ -1146,7 +1145,9 @@ static void __hwdom_init setup_one_hwdom_device(const
>> struct setup_hwdom *ctxt,
>> } while ( devfn != pdev->devfn &&
>> PCI_SLOT(devfn) == PCI_SLOT(pdev->devfn) );
>>
>> + write_lock(&ctxt->d->pci_lock);
>> err = vpci_add_handlers(pdev);
>> + write_unlock(&ctxt->d->pci_lock);
>> if ( err )
>> printk(XENLOG_ERR "setup of vPCI for d%d failed: %d\n",
>> ctxt->d->domain_id, err);
>> diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
>> index 767c1ba718..c86d33d0cd 100644
>> --- a/xen/drivers/vpci/header.c
>> +++ b/xen/drivers/vpci/header.c
>> @@ -172,6 +172,7 @@ bool vpci_process_pending(struct vcpu *v)
>> if ( rc == -ERESTART )
>> return true;
>>
>> + write_lock(&v->domain->pci_lock);
>> spin_lock(&v->vpci.pdev->vpci->lock);
>> /* Disable memory decoding unconditionally on failure. */
>> modify_decoding(v->vpci.pdev,
>> @@ -190,6 +191,7 @@ bool vpci_process_pending(struct vcpu *v)
>> * failure.
>> */
>> vpci_remove_device(v->vpci.pdev);
>> + write_unlock(&v->domain->pci_lock);
>> }
>>
>> return false;
>> @@ -201,8 +203,20 @@ static int __init apply_map(struct domain *d, const
>> struct pci_dev *pdev,
>> struct map_data data = { .d = d, .map = true };
>> int rc;
>>
>> + ASSERT(rw_is_write_locked(&d->pci_lock));
>> +
>> while ( (rc = rangeset_consume_ranges(mem, map_range, &data)) ==
>> -ERESTART )
>> + {
>> + /*
>> + * It's safe to drop and reacquire the lock in this context
>> + * without risking pdev disappearing because devices cannot be
>> + * removed until the initial domain has been started.
>> + */
>> + write_unlock(&d->pci_lock);
>> process_pending_softirqs();
>> + write_lock(&d->pci_lock);
>> + }
>> +
>> rangeset_destroy(mem);
>> if ( !rc )
>> modify_decoding(pdev, cmd, false);
>> @@ -243,6 +257,8 @@ static int modify_bars(const struct pci_dev *pdev,
>> uint16_t cmd, bool rom_only)
>> unsigned int i;
>> int rc;
>>
>> + ASSERT(rw_is_write_locked(&pdev->domain->pci_lock));
>> +
>> if ( !mem )
>> return -ENOMEM;
>>
>> @@ -522,6 +538,8 @@ static int cf_check init_bars(struct pci_dev *pdev)
>> struct vpci_bar *bars = header->bars;
>> int rc;
>>
>> + ASSERT(rw_is_write_locked(&pdev->domain->pci_lock));
>> +
>> switch ( pci_conf_read8(pdev->sbdf, PCI_HEADER_TYPE) & 0x7f )
>> {
>> case PCI_HEADER_TYPE_NORMAL:
>> diff --git a/xen/drivers/vpci/msi.c b/xen/drivers/vpci/msi.c
>> index a253ccbd7d..6ff71e5f9a 100644
>> --- a/xen/drivers/vpci/msi.c
>> +++ b/xen/drivers/vpci/msi.c
>> @@ -263,7 +263,7 @@ REGISTER_VPCI_INIT(init_msi, VPCI_PRIORITY_LOW);
>>
>> void vpci_dump_msi(void)
>> {
>> - const struct domain *d;
>> + struct domain *d;
>>
>> rcu_read_lock(&domlist_read_lock);
>> for_each_domain ( d )
>> @@ -275,6 +275,9 @@ void vpci_dump_msi(void)
>>
>> printk("vPCI MSI/MSI-X d%d\n", d->domain_id);
>>
>> + if ( !read_trylock(&d->pci_lock) )
>> + continue;
>> +
>> for_each_pdev ( d, pdev )
>> {
>> const struct vpci_msi *msi;
>> @@ -316,14 +319,33 @@ void vpci_dump_msi(void)
>> * holding the lock.
>> */
>> printk("unable to print all MSI-X entries: %d\n", rc);
>> - process_pending_softirqs();
>> - continue;
>> + goto pdev_done;
>> }
>> }
>>
>> spin_unlock(&pdev->vpci->lock);
>> + pdev_done:
>> + /*
>> + * Unlock lock to process pending softirqs. This is
>> + * potentially unsafe, as d->pdev_list can be changed in
>> + * meantime.
>> + */
>> + read_unlock(&d->pci_lock);
>> process_pending_softirqs();
>> + if ( !read_trylock(&d->pci_lock) )
>> + {
>> + printk("unable to access other devices for the domain\n");
>> + goto domain_done;
>> + }
>> }
>> + read_unlock(&d->pci_lock);
>> + domain_done:
>> + /*
>> + * We need this label at the end of the loop, but some
>> + * compilers might not be happy about label at the end of the
>> + * compound statement so we adding an empty statement here.
>> + */
>> + ;
>> }
>> rcu_read_unlock(&domlist_read_lock);
>> }
>> diff --git a/xen/drivers/vpci/msix.c b/xen/drivers/vpci/msix.c
>> index d1126a417d..b6abab47ef 100644
>> --- a/xen/drivers/vpci/msix.c
>> +++ b/xen/drivers/vpci/msix.c
>> @@ -147,6 +147,8 @@ static struct vpci_msix *msix_find(const struct domain
>> *d, unsigned long addr)
>> {
>> struct vpci_msix *msix;
>>
>> + ASSERT(rw_is_locked(&d->pci_lock));
>> +
>> list_for_each_entry ( msix, &d->arch.hvm.msix_tables, next )
>> {
>> const struct vpci_bar *bars = msix->pdev->vpci->header.bars;
>> @@ -163,7 +165,13 @@ static struct vpci_msix *msix_find(const struct domain
>> *d, unsigned long addr)
>>
>> static int cf_check msix_accept(struct vcpu *v, unsigned long addr)
>> {
>> - return !!msix_find(v->domain, addr);
>> + int rc;
>> +
>> + read_lock(&v->domain->pci_lock);
>> + rc = !!msix_find(v->domain, addr);
>> + read_unlock(&v->domain->pci_lock);
>> +
>> + return rc;
>> }
>>
>> static bool access_allowed(const struct pci_dev *pdev, unsigned long addr,
>> @@ -358,21 +366,35 @@ static int adjacent_read(const struct domain *d, const
>> struct vpci_msix *msix,
>> static int cf_check msix_read(
>> struct vcpu *v, unsigned long addr, unsigned int len, unsigned long
>> *data)
>> {
>> - const struct domain *d = v->domain;
>> - struct vpci_msix *msix = msix_find(d, addr);
>> + struct domain *d = v->domain;
>> + struct vpci_msix *msix;
>> const struct vpci_msix_entry *entry;
>> unsigned int offset;
>>
>> *data = ~0UL;
>>
>> + read_lock(&d->pci_lock);
>> +
>> + msix = msix_find(d, addr);
>> if ( !msix )
>> + {
>> + read_unlock(&d->pci_lock);
>> return X86EMUL_RETRY;
>> + }
>>
>> if ( adjacent_handle(msix, addr) )
>> - return adjacent_read(d, msix, addr, len, data);
>> + {
>> + int rc = adjacent_read(d, msix, addr, len, data);
>> +
>> + read_unlock(&d->pci_lock);
>> + return rc;
>> + }
>>
>> if ( !access_allowed(msix->pdev, addr, len) )
>> + {
>> + read_unlock(&d->pci_lock);
>> return X86EMUL_OKAY;
>> + }
>>
>> spin_lock(&msix->pdev->vpci->lock);
>> entry = get_entry(msix, addr);
>> @@ -404,6 +426,7 @@ static int cf_check msix_read(
>> break;
>> }
>> spin_unlock(&msix->pdev->vpci->lock);
>> + read_unlock(&d->pci_lock);
>>
>> return X86EMUL_OKAY;
>> }
>> @@ -491,19 +514,33 @@ static int adjacent_write(const struct domain *d,
>> const struct vpci_msix *msix,
>> static int cf_check msix_write(
>> struct vcpu *v, unsigned long addr, unsigned int len, unsigned long
>> data)
>> {
>> - const struct domain *d = v->domain;
>> - struct vpci_msix *msix = msix_find(d, addr);
>> + struct domain *d = v->domain;
>> + struct vpci_msix *msix;
>> struct vpci_msix_entry *entry;
>> unsigned int offset;
>>
>> + read_lock(&d->pci_lock);
>> +
>> + msix = msix_find(d, addr);
>> if ( !msix )
>> + {
>> + read_unlock(&d->pci_lock);
>> return X86EMUL_RETRY;
>> + }
>>
>> if ( adjacent_handle(msix, addr) )
>> - return adjacent_write(d, msix, addr, len, data);
>> + {
>> + int rc = adjacent_write(d, msix, addr, len, data);
>> +
>> + read_unlock(&d->pci_lock);
>> + return rc;
>> + }
>>
>> if ( !access_allowed(msix->pdev, addr, len) )
>> + {
>> + read_unlock(&d->pci_lock);
>> return X86EMUL_OKAY;
>> + }
>>
>> spin_lock(&msix->pdev->vpci->lock);
>> entry = get_entry(msix, addr);
>> @@ -579,6 +616,7 @@ static int cf_check msix_write(
>> break;
>> }
>> spin_unlock(&msix->pdev->vpci->lock);
>> + read_unlock(&d->pci_lock);
>>
>> return X86EMUL_OKAY;
>> }
>> diff --git a/xen/drivers/vpci/vpci.c b/xen/drivers/vpci/vpci.c
>> index 3bec9a4153..0b694beadf 100644
>> --- a/xen/drivers/vpci/vpci.c
>> +++ b/xen/drivers/vpci/vpci.c
>> @@ -38,6 +38,8 @@ extern vpci_register_init_t *const __end_vpci_array[];
>>
>> void vpci_remove_device(struct pci_dev *pdev)
>> {
>> + ASSERT(rw_is_write_locked(&pdev->domain->pci_lock));
>> +
>> if ( !has_vpci(pdev->domain) || !pdev->vpci )
>> return;
>>
>> @@ -73,6 +75,8 @@ int vpci_add_handlers(struct pci_dev *pdev)
>> const unsigned long *ro_map;
>> int rc = 0;
>>
>> + ASSERT(rw_is_write_locked(&pdev->domain->pci_lock));
>> +
>> if ( !has_vpci(pdev->domain) )
>> return 0;
>>
>> @@ -326,11 +330,12 @@ static uint32_t merge_result(uint32_t data, uint32_t
>> new, unsigned int size,
>>
>> uint32_t vpci_read(pci_sbdf_t sbdf, unsigned int reg, unsigned int size)
>> {
>> - const struct domain *d = current->domain;
>> + struct domain *d = current->domain;
>> const struct pci_dev *pdev;
>> const struct vpci_register *r;
>> unsigned int data_offset = 0;
>> uint32_t data = ~(uint32_t)0;
>> + rwlock_t *lock;
>>
>> if ( !size )
>> {
>> @@ -342,11 +347,21 @@ uint32_t vpci_read(pci_sbdf_t sbdf, unsigned int reg,
>> unsigned int size)
>> * Find the PCI dev matching the address, which for hwdom also requires
>> * consulting DomXEN. Passthrough everything that's not trapped.
>> */
>> + lock = &d->pci_lock;
>> + read_lock(lock);
>> pdev = pci_get_pdev(d, sbdf);
>> if ( !pdev && is_hardware_domain(d) )
>> + {
>> + read_unlock(lock);
>> + lock = &dom_xen->pci_lock;
>> + read_lock(lock);
>> pdev = pci_get_pdev(dom_xen, sbdf);
>> + }
>> if ( !pdev || !pdev->vpci )
>> + {
>> + read_unlock(lock);
>> return vpci_read_hw(sbdf, reg, size);
>> + }
>
> As said above in the commit message, I'm unsure you really need both
> locks, as the devices assigned to dom_xen can only be accessed by the
> hardware domain, so considering those protected by the hwdom pci_lock
> would be OK IMO. A comment would need to be added here and in
> vpci_write() to that regard.
Will do
>
> I also wonder whether you don't nest locks here like you do in
> vpci_write(). Maybe I'm missing something that justifies the
> asymmetry with the locking pattern used in vpci_write().
>
>>
>> spin_lock(&pdev->vpci->lock);
>>
>> @@ -392,6 +407,7 @@ uint32_t vpci_read(pci_sbdf_t sbdf, unsigned int reg,
>> unsigned int size)
>> ASSERT(data_offset < size);
>> }
>> spin_unlock(&pdev->vpci->lock);
>> + read_unlock(lock);
>>
>> if ( data_offset < size )
>> {
>> @@ -431,10 +447,23 @@ static void vpci_write_helper(const struct pci_dev
>> *pdev,
>> r->private);
>> }
>>
>> +/* Helper function to unlock locks taken by vpci_write in proper order */
>> +static void release_domain_write_locks(struct domain *d)
>> +{
>> + ASSERT(rw_is_write_locked(&d->pci_lock));
>> +
>> + if ( is_hardware_domain(d) )
>> + {
>> + ASSERT(rw_is_write_locked(&dom_xen->pci_lock));
>> + write_unlock(&dom_xen->pci_lock);
>> + }
>> + write_unlock(&d->pci_lock);
>> +}
>> +
>> void vpci_write(pci_sbdf_t sbdf, unsigned int reg, unsigned int size,
>> uint32_t data)
>> {
>> - const struct domain *d = current->domain;
>> + struct domain *d = current->domain;
>> const struct pci_dev *pdev;
>> const struct vpci_register *r;
>> unsigned int data_offset = 0;
>> @@ -447,8 +476,20 @@ void vpci_write(pci_sbdf_t sbdf, unsigned int reg,
>> unsigned int size,
>>
>> /*
>> * Find the PCI dev matching the address, which for hwdom also requires
>> - * consulting DomXEN. Passthrough everything that's not trapped.
>> + * consulting DomXEN. Passthrough everything that's not trapped.
>> + * If this is hwdom, we need to hold locks for both domain in case if
>> + * modify_bars() is called
>> */
>> + /*
>> + * TODO: We need to take pci_locks in exclusive mode only if we
>> + * are modifying BARs, so there is a room for improvement.
>
> Nit: could be joined with the previous comment block.
Will do
>
> Thanks, Roger.
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