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c=simple/simple; d=arm.com; s=foss; t=1779444803; bh=DNbpyntwF+hMLXGYG7QS6XgYK9N3tC6rW9pSIUZL2UQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=WnPzawxVOZEsilVN+FrmjqG+d5EGMvtws0WvCEFdP0vTh8WmzqaQCT20F6/XSKi4Y M4M+vtYWNuQY8ZNHie4OyF0sEuGltPkBQhiJ7hC+28iuovNettd25yWTfGENWI6CMX oC5xoSsmgStsFj6eIQ7W50kH7UNJLX8uN3r3m4GE= Date: Fri, 22 May 2026 11:13:17 +0100 From: Catalin Marinas To: Zeng Heng Cc: yezhenyu2@huawei.com, zhurui3@huawei.com, will@kernel.org, akpm@linux-foundation.org, npiggin@gmail.com, aneesh.kumar@kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org, wangkefeng.wang@huawei.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, David Hildenbrand , zengheng4@huawei.com Subject: Re: [PATCH] arm64: tlb: Flush walk cache when unsharing PMD tables Message-ID: References: <20260521073011.4121277-1-zengheng@huaweicloud.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 9D151160006 X-Rspamd-Server: rspam03 X-Stat-Signature: dco1np75e4b9ydcf8c1qpnk69uqxcqj9 X-HE-Tag: 1779444805-747640 X-HE-Meta: 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 v55Sq62i Wfefkq8A2gqjitfHlvqAQ0v7kThM4OvdaDbDLluxPcxtJ0VHkah/mqkoVA5I0xOPKI9pqx/SzuZoQ3Cssrh2SEHqzUdZoMm1MAsa/ZOaQmhM1zdFLKiY3H8vshwcWv7EHcLTjFjvikHFEXK3oYAQTOYWmcv9QLGO0xbYSEJeJNHY9wefevxF5HmyKXho2GjSDqq97KprQJEzCq7UrBjKCTFxWZvZKokOJOkl5MuugsYV9S9pph6ym2YvINAAr2gXrYvFWrp57w+02aU0YGfb8YZQAIQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 22, 2026 at 01:32:07PM +0800, Zeng Heng wrote: > On 2026/5/21 23:15, Catalin Marinas wrote: > > On Thu, May 21, 2026 at 04:05:07PM +0100, Catalin Marinas wrote: > > > On Thu, May 21, 2026 at 03:30:11PM +0800, Zeng Heng wrote: > > > > From: Zeng Heng > > > > > > > > When huge_pmd_unshare() is called to unshare a PMD table, the > > > > tlb_unshare_pmd_ptdesc() function sets tlb->unshared_tables=true > > > > but the aarch64 tlb_flush() only checked tlb->freed_tables to > > > > determine whether to use TLBF_NONE (vae1is, invalidates walk > > > > cache) or TLBF_NOWALKCACHE (vale1is, leaf-only). > > > > > > > > This caused the stale PMD page table entry to remain in the walk cache > > > > after unshare, potentially leading to incorrect page table walks. > > > > > > > > Fix by including unshared_tables in the check, so that when > > > > unsharing tables, TLBF_NONE is used and the walk cache is properly > > > > invalidated. > > > > > > > > Here is the detailed distinction between vae1is and vale1is: > > > > > > > > | Instruction Combination | Actual Invalidation Scope | > > > > | ------------------------ | --------------------------------------------------| > > > > | `VAE1IS` + TTL=`0` | All entries at all levels (full invalidation) | > > > > | `VAE1IS` + TTL=`2` (L2) | Non-leaf at Level 0/1 + leaf at Level 2 | > > > > | `VALE1IS` + TTL=`0` | Leaf entries at all levels (non-leaf not cleared) | > > > > | `VALE1IS` + TTL=`2` (L2) | Leaf entry at Level 2 only | > > > > > > > > Signed-off-by: Zeng Heng > > > The fix looks fine but does it need: > > > > > > Fixes: 8ce720d5bd91 ("mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather") > > > Cc: > > > > > > > --- > > > > arch/arm64/include/asm/tlb.h | 3 ++- > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h > > > > index 10869d7731b8..751bd57bc3ba 100644 > > > > --- a/arch/arm64/include/asm/tlb.h > > > > +++ b/arch/arm64/include/asm/tlb.h > > > > @@ -53,7 +53,8 @@ static inline int tlb_get_level(struct mmu_gather *tlb) > > > > static inline void tlb_flush(struct mmu_gather *tlb) > > > > { > > > > struct vm_area_struct vma = TLB_FLUSH_VMA(tlb->mm, 0); > > > > - tlbf_t flags = tlb->freed_tables ? TLBF_NONE : TLBF_NOWALKCACHE; > > > > + tlbf_t flags = (tlb->freed_tables || tlb->unshared_tables) ? > > > > + TLBF_NONE : TLBF_NOWALKCACHE; > > > > unsigned long stride = tlb_get_unmap_size(tlb); > > > > int tlb_level = tlb_get_level(tlb); > > Do we need this as well? > > The proposed fix has been validated against the issue scenarios and > works as expected. > > Per the ARM Architecture Reference Manual, whether only the last-level > page table entry is invalidated is determined by the instruction used > (vale1is for leaf entry only, vae1is for walk cache including leaf entry and > non-leaf entry), rather than the TTL field. The TTL field merely specifies > which level the leaf entry belongs to. Ah, yes, you are right. The TTL is still 2 in this case for a huge pmd, we just want the walk cache leading to it to be invalidated. So no need for the additional tlb_get_level(). Thanks. -- Catalin