Re: [PATCHv16 11/17] x86/mm/iommu/sva: Make LAM and SVA mutually exclusive

[Dmitry Vyukov]

On Sun, 12 Mar 2023 at 12:27, Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
>
> IOMMU and SVA-capable devices know nothing about LAM and only expect
> canonical addresses. An attempt to pass down tagged pointer will lead
> to address translation failure.
>
> By default do not allow to enable both LAM and use SVA in the same
> process.
>
> The new ARCH_FORCE_TAGGED_SVA arch_prctl() overrides the limitation.
> By using the arch_prctl() userspace takes responsibility to never pass
> tagged address to the device.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Reviewed-by: Ashok Raj <ashok.raj@xxxxxxxxx>
> Reviewed-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>  arch/x86/include/asm/mmu.h         | 2 ++
>  arch/x86/include/asm/mmu_context.h | 6 ++++++
>  arch/x86/include/uapi/asm/prctl.h  | 1 +
>  arch/x86/kernel/process_64.c       | 7 +++++++
>  drivers/iommu/iommu-sva.c          | 4 ++++
>  include/linux/mmu_context.h        | 7 +++++++
>  6 files changed, 27 insertions(+)
>
> diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h
> index e80762e998ce..0da5c227f490 100644
> --- a/arch/x86/include/asm/mmu.h
> +++ b/arch/x86/include/asm/mmu.h
> @@ -14,6 +14,8 @@
>  #define MM_CONTEXT_HAS_VSYSCALL                1
>  /* Do not allow changing LAM mode */
>  #define MM_CONTEXT_LOCK_LAM            2
> +/* Allow LAM and SVA coexisting */
> +#define MM_CONTEXT_FORCE_TAGGED_SVA    3
>
>  /*
>   * x86 has arch-specific MMU state beyond what lives in mm_struct.
> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
> index 06eaaf75d572..4c396e9a384f 100644
> --- a/arch/x86/include/asm/mmu_context.h
> +++ b/arch/x86/include/asm/mmu_context.h
> @@ -115,6 +115,12 @@ static inline void mm_reset_untag_mask(struct mm_struct *mm)
>         mm->context.untag_mask = -1UL;
>  }
>
> +#define arch_pgtable_dma_compat arch_pgtable_dma_compat
> +static inline bool arch_pgtable_dma_compat(struct mm_struct *mm)
> +{
> +       return !mm_lam_cr3_mask(mm) ||
> +               test_bit(MM_CONTEXT_FORCE_TAGGED_SVA, &mm->context.flags);
> +}
>  #else
>
>  static inline unsigned long mm_lam_cr3_mask(struct mm_struct *mm)
> diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
> index a31e27b95b19..eb290d89cb32 100644
> --- a/arch/x86/include/uapi/asm/prctl.h
> +++ b/arch/x86/include/uapi/asm/prctl.h
> @@ -23,5 +23,6 @@
>  #define ARCH_GET_UNTAG_MASK            0x4001
>  #define ARCH_ENABLE_TAGGED_ADDR                0x4002
>  #define ARCH_GET_MAX_TAG_BITS          0x4003
> +#define ARCH_FORCE_TAGGED_SVA          0x4004
>
>  #endif /* _ASM_X86_PRCTL_H */
> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index 88aae519c8f8..eda826a956df 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -756,6 +756,10 @@ static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned long nr_bits)
>         if (current->mm != mm)
>                 return -EINVAL;
>
> +       if (mm_valid_pasid(mm) &&
> +           !test_bit(MM_CONTEXT_FORCE_TAGGED_SVA, &mm->context.flags))
> +               return -EINTR;
> +
>         if (mmap_write_lock_killable(mm))
>                 return -EINTR;
>
> @@ -878,6 +882,9 @@ long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
>                                 (unsigned long __user *)arg2);
>         case ARCH_ENABLE_TAGGED_ADDR:
>                 return prctl_enable_tagged_addr(task->mm, arg2);
> +       case ARCH_FORCE_TAGGED_SVA:
> +               set_bit(MM_CONTEXT_FORCE_TAGGED_SVA, &task->mm->context.flags);

Hi Kirill,

ARCH_ENABLE_TAGGED_ADDR checks that task->mm == current->mm,
shouldn't ARCH_FORCE_TAGGED_SVA check that as well?

Also it looks like currently to enable both LAM and SVA.
LAM enabling checks for SVA, but SVA doesn't and both are not mutually
exclusive.


> +               return 0;
>         case ARCH_GET_MAX_TAG_BITS:
>                 if (!cpu_feature_enabled(X86_FEATURE_LAM))
>                         return put_user(0, (unsigned long __user *)arg2);
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index 4ee2929f0d7a..dd76a1a09cf7 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -2,6 +2,7 @@
>  /*
>   * Helpers for IOMMU drivers implementing SVA
>   */
> +#include <linux/mmu_context.h>
>  #include <linux/mutex.h>
>  #include <linux/sched/mm.h>
>  #include <linux/iommu.h>
> @@ -32,6 +33,9 @@ int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
>             min == 0 || max < min)
>                 return -EINVAL;
>
> +       if (!arch_pgtable_dma_compat(mm))
> +               return -EBUSY;
> +
>         mutex_lock(&iommu_sva_lock);
>         /* Is a PASID already associated with this mm? */
>         if (mm_valid_pasid(mm)) {
> diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
> index 14b9c1fa05c4..f2b7a3f04099 100644
> --- a/include/linux/mmu_context.h
> +++ b/include/linux/mmu_context.h
> @@ -35,4 +35,11 @@ static inline unsigned long mm_untag_mask(struct mm_struct *mm)
>  }
>  #endif
>
> +#ifndef arch_pgtable_dma_compat
> +static inline bool arch_pgtable_dma_compat(struct mm_struct *mm)
> +{
> +       return true;
> +}
> +#endif
> +
>  #endif
> --
> 2.39.2
>