Re: [PATCH V2 4/7] xen/virtio: Enable restricted memory access using Xen grant mappings

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Sat, 7 May 2022, Oleksandr Tyshchenko wrote:
> From: Juergen Gross <jgross@xxxxxxxx>
> 
> In order to support virtio in Xen guests add a config option XEN_VIRTIO
> enabling the user to specify whether in all Xen guests virtio should
> be able to access memory via Xen grant mappings only on the host side.
> 
> Also set PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS feature from the guest
> initialization code on Arm and x86 if CONFIG_XEN_VIRTIO is enabled.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

The patch looks OK to me

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> Changes V1 -> V2:
>    - new patch, split required changes from commit:
>     "[PATCH V1 3/6] xen/virtio: Add option to restrict memory access under 
> Xen"
>    - rework according to new platform_has() infrastructure
> ---
>  arch/arm/xen/enlighten.c     |  2 ++
>  arch/x86/xen/enlighten_hvm.c |  2 ++
>  arch/x86/xen/enlighten_pv.c  |  2 ++
>  drivers/xen/Kconfig          | 11 +++++++++++
>  include/xen/xen.h            |  8 ++++++++
>  5 files changed, 25 insertions(+)
> 
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index 07eb69f..1f9c3ba 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -443,6 +443,8 @@ static int __init xen_guest_init(void)
>       if (!xen_domain())
>               return 0;
>  
> +     xen_set_restricted_virtio_memory_access();
> +
>       if (!acpi_disabled)
>               xen_acpi_guest_init();
>       else
> diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
> index 517a9d8..8b71b1d 100644
> --- a/arch/x86/xen/enlighten_hvm.c
> +++ b/arch/x86/xen/enlighten_hvm.c
> @@ -195,6 +195,8 @@ static void __init xen_hvm_guest_init(void)
>       if (xen_pv_domain())
>               return;
>  
> +     xen_set_restricted_virtio_memory_access();
> +
>       init_hvm_pv_info();
>  
>       reserve_shared_info();
> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index 5038edb..fcd5d5d 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -109,6 +109,8 @@ static DEFINE_PER_CPU(struct tls_descs, shadow_tls_desc);
>  
>  static void __init xen_pv_init_platform(void)
>  {
> +     xen_set_restricted_virtio_memory_access();
> +
>       populate_extra_pte(fix_to_virt(FIX_PARAVIRT_BOOTMAP));
>  
>       set_fixmap(FIX_PARAVIRT_BOOTMAP, xen_start_info->shared_info);
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index 313a9127..a7bd8ce 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -339,4 +339,15 @@ config XEN_GRANT_DMA_OPS
>       bool
>       select DMA_OPS
>  
> +config XEN_VIRTIO
> +     bool "Xen virtio support"
> +     depends on VIRTIO
> +     select XEN_GRANT_DMA_OPS
> +     help
> +       Enable virtio support for running as Xen guest. Depending on the
> +       guest type this will require special support on the backend side
> +       (qemu or kernel, depending on the virtio device types used).
> +
> +       If in doubt, say n.
> +
>  endmenu
> diff --git a/include/xen/xen.h b/include/xen/xen.h
> index a99bab8..0780a81 100644
> --- a/include/xen/xen.h
> +++ b/include/xen/xen.h
> @@ -52,6 +52,14 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
>  extern u64 xen_saved_max_mem_size;
>  #endif
>  
> +#include <linux/platform-feature.h>
> +
> +static inline void xen_set_restricted_virtio_memory_access(void)
> +{
> +     if (IS_ENABLED(CONFIG_XEN_VIRTIO) && xen_domain())
> +             platform_set(PLATFORM_VIRTIO_RESTRICTED_MEM_ACCESS);
> +}
> +
>  #ifdef CONFIG_XEN_UNPOPULATED_ALLOC
>  int xen_alloc_unpopulated_pages(unsigned int nr_pages, struct page **pages);
>  void xen_free_unpopulated_pages(unsigned int nr_pages, struct page **pages);