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References: <20220330073347.3898802-1-alistair.francis@opensource.wdc.com>
In-Reply-To: <20220330073347.3898802-1-alistair.francis@opensource.wdc.com>
From:   Anup Patel <anup@brainfault.org>
Date:   Wed, 30 Mar 2022 13:22:21 +0530
Message-ID: <CAAhSdy1dSM4e_EwN8znKgkiOiV56JM=44SGpYBMBsKPp1Vxd1A@mail.gmail.com>
Subject: Re: [PATCH] riscv: Ensure only ASIDLEN is used for sfence.vma
To:     Alistair Francis <alistair.francis@opensource.wdc.com>
Cc:     linux-riscv <linux-riscv@lists.infradead.org>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>,
        Atish Patra <atishp@rivosinc.com>, Guo Ren <guoren@kernel.org>,
        Alistair Francis <alistair.francis@wdc.com>
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On Wed, Mar 30, 2022 at 1:04 PM 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.
>
> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

Instead of fixing various local_flush_tlb_xyz() functions, I suggest fixing the
__sbi_tlb_flush_range() in tlbflush.c which passes incorrect ASID.
(Refer line 45, "unsigned long asid = atomic_long_read(&mm->context.id);")

Also, please add the "Fixes: " tag.

Regards,
Anup

> ---
>  arch/riscv/mm/context.c  | 2 +-
>  arch/riscv/mm/tlbflush.c | 4 ++--
>  include/linux/mm_types.h | 2 ++
>  3 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> index 7acbfbd14557..4329fe54176b 100644
> --- a/arch/riscv/mm/context.c
> +++ b/arch/riscv/mm/context.c
> @@ -22,7 +22,7 @@ DEFINE_STATIC_KEY_FALSE(use_asid_allocator);
>
>  static unsigned long asid_bits;
>  static unsigned long num_asids;
> -static unsigned long asid_mask;
> +unsigned long asid_mask;
>
>  static atomic_long_t current_version;
>
> diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> index 37ed760d007c..4469615aa07f 100644
> --- a/arch/riscv/mm/tlbflush.c
> +++ b/arch/riscv/mm/tlbflush.c
> @@ -10,7 +10,7 @@ static inline void local_flush_tlb_all_asid(unsigned long asid)
>  {
>         __asm__ __volatile__ ("sfence.vma x0, %0"
>                         :
> -                       : "r" (asid)
> +                       : "r" (asid & asid_mask)
>                         : "memory");
>  }
>
> @@ -19,7 +19,7 @@ static inline void local_flush_tlb_page_asid(unsigned long addr,
>  {
>         __asm__ __volatile__ ("sfence.vma %0, %1"
>                         :
> -                       : "r" (addr), "r" (asid)
> +                       : "r" (addr), "r" (asid & asid_mask)
>                         : "memory");
>  }
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 8834e38c06a4..5fa7cc0af853 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -666,6 +666,8 @@ struct mm_struct {
>
>  extern struct mm_struct init_mm;
>
> +extern unsigned long asid_mask;
> +
>  /* Pointer magic because the dynamic array size confuses some compilers. */
>  static inline void mm_init_cpumask(struct mm_struct *mm)
>  {
> --
> 2.35.1
>