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
>
