From: sashiko-bot@kernel.org
To: "Yunhui Cui" <cuiyunhui@bytedance.com>
Cc: kvm@vger.kernel.org, linux-perf-users@vger.kernel.org
Subject: Re: [PATCH v2 14/15] riscv/mm: optimize mprotect for Svnapot mappings
Date: Thu, 16 Jul 2026 13:07:05 +0000 [thread overview]
Message-ID: <20260716130705.A94691F00A3D@smtp.kernel.org> (raw)
In-Reply-To: <8b79ddc3311e1dc32b150b7efbaed5a187ee5ccd.1784201104.git.cuiyunhui@bytedance.com>
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The fallback path corrupts userspace memory tracking by erroneously injecting `_PAGE_SOFT_DIRTY` via `pte_mkdirty()`.
--
--- Patch [14]: [PATCH v2 14/15] riscv/mm: optimize mprotect for Svnapot mappings ---
commit f75eddb541d9ba388068a3cbeef6571534eb416b
Author: Yunhui Cui <cuiyunhui@bytedance.com>
riscv/mm: optimize mprotect for Svnapot mappings
This commit optimizes mprotect operations for Svnapot mappings by handling
full blocks in a single batched operation. A fallback loop is retained for
partial, unaligned, or otherwise inconsistent mappings.
> diff --git a/arch/riscv/mm/contpte.c b/arch/riscv/mm/contpte.c
> index 8289f39d6e188..6a1156629d115 100644
> --- a/arch/riscv/mm/contpte.c
> +++ b/arch/riscv/mm/contpte.c
[ ... ]
> +pte_t modify_prot_start_ptes(struct vm_area_struct *vma, unsigned long addr,
> + pte_t *ptep, unsigned int nr)
> +{
> + struct mm_struct *mm = vma->vm_mm;
> + unsigned long ptent_addr;
> + pte_t raw, pte, ptent;
> + unsigned int i;
> +
> + if (napotpte_can_modify_prot_block(mm, addr, ptep, nr, &raw)) {
[ ... ]
> + if (pte_dirty(ptent))
> + pte = riscv_pte_mkhwdirty(pte);
[ ... ]
> + return pte;
> + }
> +
> + pte = __ptep_modify_prot_start(vma, addr, ptep);
> + while (--nr) {
> + ptep++;
> + addr += PAGE_SIZE;
> + ptent = __ptep_modify_prot_start(vma, addr, ptep);
> + if (pte_dirty(ptent))
> + pte = pte_mkdirty(pte);
[Severity: Medium]
Does this fallback path unintentionally set the soft-dirty bit for userspace
tracking?
On RISC-V, pte_mkdirty() sets both the hardware _PAGE_DIRTY bit and the
userspace-visible _PAGE_SOFT_DIRTY bit. If a Svnapot mapping was previously
written to (hardware dirty) but its soft-dirty bit was explicitly cleared by
userspace (e.g. via /proc/pid/clear_refs), calling mprotect() on a partial
or unaligned segment of this block triggers this fallback path.
Since the fallback path uses pte_mkdirty() to accumulate the dirty state, it
would inadvertently re-set the _PAGE_SOFT_DIRTY bit on the final batched PTE.
Userspace tracking tools like CRIU could subsequently falsely record this
memory as modified.
The fast path correctly uses riscv_pte_mkhwdirty(pte) to avoid this exact
issue. Should this loop also use riscv_pte_mkhwdirty(pte) instead of
pte_mkdirty(pte)?
> + if (pte_young(ptent))
> + pte = pte_mkyoung(pte);
> + }
> +
> + return pte;
> +}
--
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1784201104.git.cuiyunhui@bytedance.com?part=14
next prev parent reply other threads:[~2026-07-16 13:07 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-16 12:41 [PATCH v2 00/15] riscv: add Svnapot PTE folding support Yunhui Cui
2026-07-16 12:41 ` [PATCH v2 01/15] riscv: introduce raw PTE helpers Yunhui Cui
2026-07-16 12:59 ` sashiko-bot
2026-07-16 12:41 ` [PATCH v2 02/15] riscv: switch arch page-table users to " Yunhui Cui
2026-07-16 13:05 ` sashiko-bot
2026-07-16 12:41 ` [PATCH v2 03/15] riscv/mm: implement Svnapot contpte read-side helpers Yunhui Cui
2026-07-16 12:59 ` sashiko-bot
2026-07-16 12:41 ` [PATCH v2 04/15] riscv/mm: implement Svnapot contpte update helpers Yunhui Cui
2026-07-16 13:03 ` sashiko-bot
2026-07-16 12:41 ` [PATCH v2 05/15] mm: extend pte batch and leaf-size helpers Yunhui Cui
2026-07-16 13:06 ` sashiko-bot
2026-07-16 12:41 ` [PATCH v2 06/15] riscv: make pte_batch_hint() honor folio batch flags Yunhui Cui
2026-07-16 12:41 ` [PATCH v2 07/15] riscv/mm: preserve Svnapot leaf-size semantics for page-table consumers Yunhui Cui
2026-07-16 12:57 ` sashiko-bot
2026-07-16 12:41 ` [PATCH v2 08/15] riscv/mm: avoid redundant Svnapot A/D aggregation Yunhui Cui
2026-07-16 12:41 ` [PATCH v2 09/15] riscv/mm: avoid Svnapot consistency checks in ptep_get() Yunhui Cui
2026-07-16 13:03 ` sashiko-bot
2026-07-16 12:41 ` [PATCH v2 10/15] mm/gup: add fast-GUP specific lockless PTE helpers Yunhui Cui
2026-07-16 12:41 ` [PATCH v2 11/15] riscv: mm: avoid Svnapot A/D aggregation in fast-GUP Yunhui Cui
2026-07-16 12:41 ` [PATCH v2 12/15] arm64: mm: avoid contpte " Yunhui Cui
2026-07-16 12:41 ` [PATCH v2 13/15] riscv/mm: remove redundant TLB flush in napotpte_convert Yunhui Cui
2026-07-16 13:17 ` sashiko-bot
2026-07-16 12:41 ` [PATCH v2 14/15] riscv/mm: optimize mprotect for Svnapot mappings Yunhui Cui
2026-07-16 13:07 ` sashiko-bot [this message]
2026-07-16 12:41 ` [PATCH v2 15/15] riscv: mm: Request large exec folios for Svnapot Yunhui Cui
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