Re: [XEN PATCH v12 2/7] x86/pvh: Allow (un)map_pirq when dom0 is PVH

["Chen, Jiqian" <Jiqian.Chen@xxxxxxx>]

On 2024/7/31 15:50, Roger Pau Monné wrote:
> On Mon, Jul 08, 2024 at 07:41:19PM +0800, Jiqian Chen wrote:
>> If run Xen with PVH dom0 and hvm domU, hvm will map a pirq for
>> a passthrough device by using gsi, see qemu code
>> xen_pt_realize->xc_physdev_map_pirq and libxl code
>> pci_add_dm_done->xc_physdev_map_pirq. Then xc_physdev_map_pirq
>> will call into Xen, but in hvm_physdev_op, PHYSDEVOP_map_pirq
>> is not allowed because currd is PVH dom0 and PVH has no
>> X86_EMU_USE_PIRQ flag, it will fail at has_pirq check.
>>
>> So, allow PHYSDEVOP_map_pirq when dom0 is PVH and also allow
>> PHYSDEVOP_unmap_pirq for the removal device path to unmap pirq.
>> And add a new check to prevent (un)map when the subject domain
>> doesn't have a notion of PIRQ.
>>
>> So that the interrupt of a passthrough device can be
>> successfully mapped to pirq for domU with a notion of PIRQ
>> when dom0 is PVH
>>
>> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
>> Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
>> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
>> ---
>>  xen/arch/x86/hvm/hypercall.c |  6 ++++++
>>  xen/arch/x86/physdev.c       | 12 ++++++++++--
>>  2 files changed, 16 insertions(+), 2 deletions(-)
>>
>> diff --git a/xen/arch/x86/hvm/hypercall.c b/xen/arch/x86/hvm/hypercall.c
>> index 0fab670a4871..03ada3c880bd 100644
>> --- a/xen/arch/x86/hvm/hypercall.c
>> +++ b/xen/arch/x86/hvm/hypercall.c
>> @@ -71,8 +71,14 @@ long hvm_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
>> arg)
>>  
>>      switch ( cmd )
>>      {
>> +        /*
>> +        * Only being permitted for management of other domains.
>> +        * Further restrictions are enforced in do_physdev_op.
>> +        */
>>      case PHYSDEVOP_map_pirq:
>>      case PHYSDEVOP_unmap_pirq:
>> +        break;
>> +
>>      case PHYSDEVOP_eoi:
>>      case PHYSDEVOP_irq_status_query:
>>      case PHYSDEVOP_get_free_pirq:
>> diff --git a/xen/arch/x86/physdev.c b/xen/arch/x86/physdev.c
>> index d6dd622952a9..9f30a8c63a06 100644
>> --- a/xen/arch/x86/physdev.c
>> +++ b/xen/arch/x86/physdev.c
>> @@ -323,7 +323,11 @@ ret_t do_physdev_op(int cmd, 
>> XEN_GUEST_HANDLE_PARAM(void) arg)
>>          if ( !d )
>>              break;
>>  
>> -        ret = physdev_map_pirq(d, map.type, &map.index, &map.pirq, &msi);
>> +        /* Only mapping when the subject domain has a notion of PIRQ */
>> +        if ( !is_hvm_domain(d) || has_pirq(d) )
> 
> I'm afraid this is not true.  It's fine to map interrupts to HVM
> domains that don't have XENFEAT_hvm_pirqs enabled.  has_pirq() simply
> allow HVM domains to route interrupts from devices (either emulated or
> passed through) over event channels.
> 
> It might have worked in the past (when using a version of Xen < 4.19)
> because XENFEAT_hvm_pirqs was enabled by default for HVM guests.
> 
> physdev_map_pirq() will work fine when used against domains that don't
> have XENFEAT_hvm_pirqs enabled, and it needs to be kept this way.
> 
> I think you want to allow PHYSDEVOP_{,un}map_pirq for HVM domains, but
> keep the code in do_physdev_op() as-is.  You will have to check
> whether the current paths in do_physdev_op() are not making
> assumptions about XENFEAT_hvm_pirqs being enabled when the calling
> domain is of HVM type.  I don't think that's the case, but better
> check.
If I understand correctly, you also talked about preventing self-mapping when 
the domain is HVM type and doesn't has XENFEAT_hvm_pirqs.
Change to this?
        if ( !is_hvm_domain(d) || has_pirq(d) || d != currd )
            ret = physdev_map_pirq(d, map.type, &map.index, &map.pirq, &msi);
        else
            ret = -EOPNOTSUPP;

> 
> Thanks, Roger.

-- 
Best regards,
Jiqian Chen.