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SubjectRe: [PATCH v3] riscv: Ensure only ASIDLEN is used for sfence.vma
On Thu, Mar 31, 2022 at 11:29 AM Alistair Francis
<alistair.francis@opensource.wdc.com> wrote:
>
> From: Alistair Francis <alistair.francis@wdc.com>
>
> When we set the value of context.id using __new_context() we set both
> the asid and the current_version with this return statement in
> __new_context():
>
> return asid | ver;
>
> This means that when local_flush_tlb_all_asid() is called with the asid
> specified from context.id we can write the incorrect value.
>
> We get away with this as hardware ignores the extra bits, as the RISC-V
> specification states:
>
> "bits SXLEN-1:ASIDMAX of the value held in rs2 are reserved for future
> standard use. Until their use is defined by a standard extension, they
> should be zeroed by software and ignored by current implementations."
>
> but it is still a bug and worth addressing as we are incorrectly setting
> extra bits.
>
> This patch uses asid_mask when calling sfence.vma to ensure the asid is
> always the correct len (ASIDLEN). This is similar to what we do in
> arch/riscv/mm/context.c.
>
> Fixes: 3f1e782998cd ("riscv: add ASID-based tlbflushing methods")
> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

Looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup

> ---
> v3:
> - Use helper function
> v2:
> - Pass in pre-masked value
>
> arch/riscv/include/asm/mmu_context.h | 2 ++
> arch/riscv/mm/context.c | 5 +++++
> arch/riscv/mm/tlbflush.c | 2 +-
> 3 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h
> index 7030837adc1a..94e82c9e17eb 100644
> --- a/arch/riscv/include/asm/mmu_context.h
> +++ b/arch/riscv/include/asm/mmu_context.h
> @@ -16,6 +16,8 @@
> void switch_mm(struct mm_struct *prev, struct mm_struct *next,
> struct task_struct *task);
>
> +unsigned long get_mm_asid(struct mm_struct *mm);
> +
> #define activate_mm activate_mm
> static inline void activate_mm(struct mm_struct *prev,
> struct mm_struct *next)
> diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> index 7acbfbd14557..14aec5bacbc1 100644
> --- a/arch/riscv/mm/context.c
> +++ b/arch/riscv/mm/context.c
> @@ -302,6 +302,11 @@ static inline void flush_icache_deferred(struct mm_struct *mm, unsigned int cpu)
> #endif
> }
>
> +unsigned long get_mm_asid(struct mm_struct *mm)
> +{
> + return atomic_long_read(&mm->context.id) & asid_mask;
> +}
> +
> void switch_mm(struct mm_struct *prev, struct mm_struct *next,
> struct task_struct *task)
> {
> diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> index 37ed760d007c..9c89c4951bee 100644
> --- a/arch/riscv/mm/tlbflush.c
> +++ b/arch/riscv/mm/tlbflush.c
> @@ -42,7 +42,7 @@ static void __sbi_tlb_flush_range(struct mm_struct *mm, unsigned long start,
> /* check if the tlbflush needs to be sent to other CPUs */
> broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
> if (static_branch_unlikely(&use_asid_allocator)) {
> - unsigned long asid = atomic_long_read(&mm->context.id);
> + unsigned long asid = get_mm_asid(mm);
>
> if (broadcast) {
> sbi_remote_sfence_vma_asid(cmask, start, size, asid);
> --
> 2.35.1
>

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