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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=NMLyfmu+3qgBioBF8DPIpA0YdV971kcjPpR8H9920pmFHpKx+W8EpM4oJyHFyKev5 yF0OlMWEphWAWXlnh8EIKY6K7Eg4mD58l+bMnr+4DDyVpSpX81cwoSsqg8a0Z8W8oc ipF3rlY/vHHH/M4U3q6PK9OOFRQm9ikxZsahEc1Y= Message-ID: Date: Fri, 30 Oct 2026 19:50:38 +0530 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 03/10] mm/vmalloc: clamp an unaligned range in vunmap_pte_range() To: Hao Ge Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, Sashiko , "Ritesh Harjani (IBM)" , Shrikanth Hegde , Alexander Potapenko , Marco Elver , Dmitry Vyukov , Andrew Morton , Dennis Zhou , Tejun Heo , Christoph Lameter , Uladzislau Rezki , Suren Baghdasaryan , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" References: <20261026080329.140244-1-hao.ge@linux.dev> <20261026080329.140244-4-hao.ge@linux.dev> <99f529e8-06f7-4a20-a60b-0330c5d3d91c@arm.com> <5452d555-82f9-45a6-b443-ee732b1874ba@linux.dev> Content-Language: en-US From: Dev Jain In-Reply-To: <5452d555-82f9-45a6-b443-ee732b1874ba@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 2E12C10000E X-Stat-Signature: d4g6udq3sghjhum46e369d981rwdocey X-Rspam-User: X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793370049-405173 X-HE-Meta: U2FsdGVkX1+O8HBpIV4BGEiMbrDf8E9MkvVghdGBOBQaso0LL4jFHQd6P/av4Jiv029DOoKWekN1kddmSFo8QndwpBy3A8eBlBJKlsKF51Q1Z9cDnNO8YD8/b+JrEwnheDXMKxMZEFboVn/ALfxEBL/IU8YMovMAUKh786G9Dbn+O6k4VaDvp7QHTLUJ/5D0z9e84XyV+xPzVt5RkAN0ivvDz/7unok1RHyRbV8/aD34YC6zeXmB5Mk4Fr5TR5w7E1NRewRnGxzEqewrTLG+mv5eYeKM2v0gpTz8HwtEo3geZWrTirsazdfFGHCBmX5qBStbgH7F6LeOHmXOW/dmGmwMDuKo5tr2N/xi4u+8pohsrs1XZUEqQIZd5hauq6T7b4CsdoVj45amOHFharr86mEt0g3QS0hj/NOK8YP9T1KP9D5VUFOCFi8qVULkx39kDzIi9UyGqH7Kwpe71zOuUQYMGgm+NLRG3pi/ucokeMYIzenHtHOhEGYzI4yy3eSa6vt2DHzsc9XVK2XLvUdUiYM8EPH7z9C1vsqwAkdTHkDOcMK711vXUaUEKoVM+YtLkBZL8m/+VQxsRBPGzdb++rvj0gl+C7nn1ZRx/zvQotr+sIMGNyw/gb7chO0Jv04Hb7o/KFANU0i3EDHbHNuctxHbbJZpeU/CzkHV8/SR49jQvtn16pwPTQnzmAKO35wcIumgRu1R8KJpERSRhk3lRyVgbfUfqGgdHKZ4pqARAiPlZkZBY4rT7Q0QRHEtR01IQnHv/SMSdhO5fvxxyRgwi8RICFydod/93HhNmREJ5MnOWrsuPNdFhHwoRerdcudFwGR3bRYrt46vMlrwdB4ImvlLsp2WqY5KFYKOza5SG7bRFqcgVidi/bx77340yMpUqgVtWsiGrAO3BLQw/yOP9uH4lihqjGfU4u41UVwLqRPGhNIrIOvgDtFSSoQsP/sxKt/Zsvzxw2FOuJvgQMA Gy3YzyIc +KnjaRtGC+mngSATHgUSiWYgwhVK0jDmbLaKEHJjUJPBSLDLwz3Nr7UFvBpOYBMIe46/drlQp7mUB1CADqDzy+bVH0/kQkRQ18xMMBhiyyoApBWdF7rwxt6Rj7nGqPINlA0x9p4c3bx2E4VkQC1SqyaCZ+R+ie9JYh0m9Ry9OOxTmUNLVAbgthJo9sQRD5OXdPBrmQ51Yv8p50wbE6XCXOiBXux1tBWuPxyUbVWqoJSLbZCip5ZM1ZL8f6KSXhF2NWED2iZXk2/TzK2IMGC5fTZNjpjf0z2xgHlmOfGYrrUC34yDA1m9xMZpSYh/Ll05daIt5pP59AXQkHYNf5zzKSkqEWz1l0s7t5yCEpnOVNI+MUcKOB0aUHWj+aLs7alXlUb4r Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 30/10/26 2:00 pm, Hao Ge wrote: > Hi Dev > > Thanks for your review. > > On 2026/10/30 15:14, Dev Jain wrote: >> >> >> On 26/10/26 1:33 pm, Hao Ge wrote: >>> commit a739e6b557af ("mm: vmalloc: WARN_ON if mapping size is not >>> PAGE_SIZE aligned") made vmap_pte_range() warn and bail out when the >>> size is not a multiple of PAGE_SIZE. That loop steps in page >> >> Why are we checking the alignment so late into vmap_pte_range? Why not >> simply do >> >> if (!IS_ALIGNED(addr, PAGE_SIZE) || !IS_ALIGNED(end, PAGE_SIZE)) >> return; (or return -EINVAL); >> >> at the start of vmap_range_noflush and vunmap_range_noflush? > > I think adding that check at the entry of vunmap_range_noflush() > goes against its design intent. Its job is to tear down the mappings > of the given VA range, so even when the caller passes a size that is > not page-aligned, we still have to unmap whatever is mapped within > that range. > > So the patch clamps end down to the last full page and keeps > clearing. A buggy caller still gets its mapping torn down as far as > it goes, and nothing is left behind. The check here is just for > protection. > > This is just my preliminary understanding; I may be mistaken. Hmm I get you, but this is very ugly. We are trying to tolerate a blatant bug in the caller with not-so-nice code. But see below. > > Thanks > Best Regards > Hao > > > But that's just my understanding, happy to be corrected. > > >> >> >>> multiples and stops only at addr == end; with an unaligned size addr >>> never lands on end, so the loop cannot terminate and walks off the >>> end of the page table. >>> >>> vunmap_pte_range() has the same loop without any guard, so an >>> unaligned range would clear PTEs past end without ever stopping, >>> walking off the end of the page table. >>> >>> Add the check there too. The range is clamped down to the last full >>> page rather than dropped, and the loop is skipped when nothing is >>> left, so a buggy caller still gets its PTEs cleared as far as they >>> go. >>> >>> Reported-by: Sashiko >>> Signed-off-by: Hao Ge >>> --- >>> mm/vmalloc.c | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c >>> index 44e0eb32708f..7131f60d1a8e 100644 >>> --- a/mm/vmalloc.c >>> +++ b/mm/vmalloc.c >>> @@ -393,6 +393,11 @@ static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, >>> pte_t ptent; >>> unsigned long size = PAGE_SIZE; >>> >>> + if (WARN_ON_ONCE(!PAGE_ALIGNED(end - addr))) >>> + end = addr + PAGE_ALIGN_DOWN(end - addr); For simplicity assume PAGE_SIZE is 4, start is 3, end is 10. With your code we will get addr = 3, end = 3 + ALIGN_DOWN(10 - 3) = 3 + 4 = 7. So the range becomes [3, 7) clearing only two ptes, the one covering [0, 3], the second covering [4, 7]. I feel we should rather make the range from [3, 10] to [0, 11], clearing three ptes. So, at the start of vunmap_range_noflush we could basically WARN_ON on non-alignment, and then clamp the start down, and clamp the end up to PAGE_SIZE. And with this also throw in a patch to bring the -EINVAL bailout in vmap_pte_range to the top, in vmap_range_noflush and check both start and end alignment. >>> + if (end == addr) >>> + return; >>> + >>> pte = pte_offset_kernel(pmd, addr); >>> lazy_mmu_mode_enable(); >>> >>