Re: [RFC PATCH 4/6] virtio: Various updates to xen-virtio DMA ops layer

[Oleksandr <olekstysh@xxxxxxxxx>]

Hello Stefano, Juergen


On 19.04.22 09:58, Juergen Gross wrote:
> On 18.04.22 21:11, Stefano Stabellini wrote:
> > On Sun, 17 Apr 2022, Oleksandr wrote:
> > > On 16.04.22 01:02, Stefano Stabellini wrote:
> > > > On Thu, 14 Apr 2022, Oleksandr Tyshchenko wrote:
> > > > > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> > > > >
> > > > > In the context of current patch do the following:
> > > > > 1. Update code to support virtio-mmio devices
> > > > > 2. Introduce struct xen_virtio_data and account passed virtio devices
> > > > >      (using list) as we need to store some per-device data
> > > > > 3. Add multi-page support for xen_virtio_dma_map(unmap)_page 
> > > > > callbacks
> > > > > 4. Harden code against malicious backend
> > > > > 5. Change to use alloc_pages_exact() instead of __get_free_pages()
> > > > > 6. Introduce locking scheme to protect mappings (I am not 100% sure
> > > > >      whether per-device lock is really needed)
> > > > > 7. Handle virtio device's DMA mask
> > > > > 8. Retrieve the ID of backend domain from DT for virtio-mmio device
> > > > >      instead of hardcoding it.
> > > > >
> > > > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> > > > > ---
> > > > >    arch/arm/xen/enlighten.c |  11 +++
> > > > >    drivers/xen/Kconfig      |   2 +-
> > > > >    drivers/xen/xen-virtio.c | 200
> > > > > ++++++++++++++++++++++++++++++++++++++++++-----
> > > > >    include/xen/xen-ops.h    |   5 ++
> > > > >    4 files changed, 196 insertions(+), 22 deletions(-)
> > > > >
> > > > > diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> > > > > index ec5b082..870d92f 100644
> > > > > --- a/arch/arm/xen/enlighten.c
> > > > > +++ b/arch/arm/xen/enlighten.c
> > > > > @@ -409,6 +409,17 @@ int __init arch_xen_unpopulated_init(struct 
> > > > > resource
> > > > > **res)
> > > > >    }
> > > > >    #endif
> > > > >    +#ifdef CONFIG_ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS
> > > > > +int arch_has_restricted_virtio_memory_access(void)
> > > > > +{
> > > > > +    if (IS_ENABLED(CONFIG_XEN_HVM_VIRTIO_GRANT) && xen_hvm_domain())
> > > > > +        return 1;
> > > > Instead of xen_hvm_domain(), you can just use xen_domain(). Also there
> > > > is no need for the #ifdef
> > > > CONFIG_ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS, given that:
> > > >
> > > > CONFIG_XEN_HVM_VIRTIO_GRANT depends on XEN_VIRTIO which selects
> > > > ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS
> > >
> > > Yes, but please see my comments in commit #2 regarding
> > > CONFIG_XEN_HVM_VIRTIO_GRANT option and
> > > arch_has_restricted_virtio_memory_access() on Arm.
> > >
> > > I propose to have the following on Arm:
> > >
> > > int arch_has_restricted_virtio_memory_access(void)
> > > {
> > >       return xen_has_restricted_virtio_memory_access();
> > > }
> > >
> > >
> > > where common xen.h contain a helper to be used by both Arm and x86:
> > >
> > > static inline int xen_has_restricted_virtio_memory_access(void)
> > > {
> > >       if (IS_ENABLED(CONFIG_XEN_VIRTIO) && (xen_pv_domain() ||
> > > xen_hvm_domain()))
> > >           return 1;
> > >
> > >       return 0;
> > > }
> > >
> > >
> > > But I would be happy with what you propose as well.
> > As I wrote in the previous reply, I also prefer to share the code
> > between x86 and ARM, and I think it could look like:
> >
> > int arch_has_restricted_virtio_memory_access(void)
> > {
> >       return xen_has_restricted_virtio_memory_access();
> > }
> > [...]
> > static inline int xen_has_restricted_virtio_memory_access(void)
> > {
> >       return (IS_ENABLED(CONFIG_XEN_VIRTIO) && xen_domain());
> > }
> >
> > But let's check with Juergen and Boris.

for the record, it is already clarified in commit #2, I will use this 
variant.

> > > > > +    return 0;
> > > > > +}
> > > > > +EXPORT_SYMBOL_GPL(arch_has_restricted_virtio_memory_access);
> > > > > +#endif
> > > > > +
> > > > >    static void __init xen_dt_guest_init(void)
> > > > >    {
> > > > >        struct device_node *xen_node;
> > > > > diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> > > > > index fc61f7a..56afe6a 100644
> > > > > --- a/drivers/xen/Kconfig
> > > > > +++ b/drivers/xen/Kconfig
> > > > > @@ -347,7 +347,7 @@ config XEN_VIRTIO
> > > > >      config XEN_HVM_VIRTIO_GRANT
> > > > >        bool "Require virtio for fully virtualized guests to use grant
> > > > > mappings"
> > > > > -    depends on XEN_VIRTIO && X86_64
> > > > > +    depends on XEN_VIRTIO && (X86_64 || ARM || ARM64)
> > > > you can remove the architectural dependencies
> > >
> > > According to the conversation in commit #2 we are considering just a 
> > > single
> > > XEN_VIRTIO option, but it is going to has the
> > > same architectural dependencies: (X86_64 || ARM || ARM64)
> > >
> > > By removing the architectural dependencies here, we will leave also 
> > > X86_32
> > > covered (neither XEN_HVM_VIRTIO_GRANT nor XEN_PV_VIRTIO covered it). 
> > > I don't
> > > know whether it is ok or not.
> > >
> > > Shall I remove dependencies anyway?
> > No, good point. I don't know about X86_32. This is another detail where
> > Juergen or Boris should comment.
> X86_32 should in theory work (it is HVM/PVH only, as PV 32-bit guests 
> are no
> longer supported).

ok, thank you for confirming. I will drop architectural dependencies then.


> Juergen
--
Regards,

Oleksandr Tyshchenko