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

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Date:   Wed, 23 Jun 2021 12:28:21 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Will Deacon <will@...nel.org>
Cc:     Zhenyu Ye <yezhenyu2@...wei.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 12:04:12PM +0100, Will Deacon wrote:
> 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.

If you haven't queued it already, feel free to add:

Acked-by: Catalin Marinas <catalin.marinas@....com>

I'd also add:

Cc: <stable@...r.kernel.org> # 5.9.x

-- 
Catalin