linux-kernel - Re: [PATCH v1] arm64: tlb: fix the TTL value of tlb_get

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Date:   Wed, 23 Jun 2021 12:04:12 +0100
From:   Will Deacon <will@...nel.org>
To:     Zhenyu Ye <yezhenyu2@...wei.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        aneesh.kumar@...ux.ibm.com, Marc Zyngier <maz@...nel.org>,
        steven.price@....com, Peter Zijlstra <peterz@...radead.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        Xiexiangyou <xiexiangyou@...wei.com>, liushixin2@...wei.com,
        huyaqin <huyaqin1@...wei.com>, zhurui3@...wei.com
Subject: Re: [PATCH v1] arm64: tlb: fix the TTL value of tlb_get_level

On Wed, Jun 23, 2021 at 03:05:22PM +0800, Zhenyu Ye wrote:
> The TTL field indicates the level of page table walk holding the *leaf*
> entry for the address being invalidated. But currently, the TTL field
> may be set to an incorrent value in the following stack:
> 
> pte_free_tlb
>     __pte_free_tlb
>         tlb_remove_table
>             tlb_table_invalidate
>                 tlb_flush_mmu_tlbonly
>                     tlb_flush
> 
> In this case, we just want to flush a PTE page, but the tlb->cleared_pmds
> is set and we get tlb_level = 2 in the tlb_get_level() function. This may
> cause some unexpected problems.
> 
> This patch set the TTL field to 0 if tlb->freed_tables is set. The
> tlb->freed_tables indicates page table pages are freed, not the leaf
> entry.
> 
> Fixes: c4ab2cbc1d87 ("arm64: tlb: Set the TTL field in flush_tlb_range")
> Reported-by: ZhuRui <zhurui3@...wei.com>
> Signed-off-by: Zhenyu Ye <yezhenyu2@...wei.com>
> ---
>  arch/arm64/include/asm/tlb.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
> index 61c97d3b58c7..c995d1f4594f 100644
> --- a/arch/arm64/include/asm/tlb.h
> +++ b/arch/arm64/include/asm/tlb.h
> @@ -28,6 +28,10 @@ static void tlb_flush(struct mmu_gather *tlb);
>   */
>  static inline int tlb_get_level(struct mmu_gather *tlb)
>  {
> +	/* The TTL field is only valid for the leaf entry. */
> +	if (tlb->freed_tables)
> +		return 0;
> +
>  	if (tlb->cleared_ptes && !(tlb->cleared_pmds ||
>  				   tlb->cleared_puds ||
>  				   tlb->cleared_p4ds))

Thanks. I can't see a better way around this, so I'll queue the patch.
The stage-2 page-table code looks ok afaict, but please can you check it
too?

Cheers,

Will