From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A51AB42A783; Tue, 28 Jul 2026 13:08:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785244097; cv=none; b=PeUZqrbaS6Fd76xELxfj0xckqhJ5VUwAAtUAVJy0QrFoCYcySKTqzVBqc8e1aN1YERzHCrznVIExDZ3TtLSIoVcwffgLUxxMZCY/ZqWD+ZWtGbYyKgrjztunnTD0VOHd8WJYWewfuA/LMvG4NKg6yJ4RryuciFnCjOmV7e7QI5s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785244097; c=relaxed/simple; bh=BVvgZ9I2afzRj2pvRPqY8IpwPLGhMReUR6M1hcqsb0k=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=sQe9iZPPNtaQ+VIm42uJux9+BFb5dqvAEt4zfZsSz0JOZql0YFCjlZaHB5qWVGhLhOyHiflWIZspTi8QnL8HnUF21gAMz7yB/zBbmLMcy0OZnjADQHQY+/pjsov8K6t++L7Cmw4acRlWz3IWFAAeU5V/us4elk6SOQ+B/3fWBbk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cu9QmqSd; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="cu9QmqSd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7FB9F1F000E9; Tue, 28 Jul 2026 13:08:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785244096; bh=G7MX1MGs508cUN6xCRbAVP0KOcolddHw8KtRR6TuHhw=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=cu9QmqSd9G58fcL+OkxtnXYi5TguTf11LIFRpQcrMpgkr3ZIKGUAgohguxAsP5yBD dOtfjxqdPowbwzzowZCPOVPXebaq0SLKt5fmnWoyH8h/lXldJZguBcmC7R6J885fko HRHW1AmWOLY7jp5F3FX/NfnitzaSCEHG9IyIwHYE1Thk30U4kQgPZNH8AxlNLStsPP Pw92SA8PCmod5jXAsZmHQv/vnpBVOnu+UBtFK4XFk+ONXxWt2x+8stOH5XFsYUpzUg A79VyG6JgiVkANaGRmVOWu2v5EZHOkEog/3syRkQrxd8+AaWSRtLjdbKavBPNYlWMO 9idT1MzaBv9jw== From: "Mike Rapoport (Microsoft)" Date: Tue, 28 Jul 2026 16:07:44 +0300 Subject: [PATCH 1/5] x86/mm/pat: introcude cpa_lock() and cpa_unlock() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260728-cpa-fixes-v1-1-2ed2352300b3@kernel.org> References: <20260728-cpa-fixes-v1-0-2ed2352300b3@kernel.org> In-Reply-To: <20260728-cpa-fixes-v1-0-2ed2352300b3@kernel.org> To: Dave Hansen Cc: Andrew Morton , Andy Lutomirski , Borislav Petkov , David CARLIER , David Hildenbrand , Ingo Molnar , Jason Gunthorpe , Juergen Gross , Kevin Tian , Kiryl Shutsemau , "Liam R. Howlett" , Lorenzo Stoakes , Lu Baolu , Mike Rapoport , "H. Peter Anvin" , Peter Zijlstra , Shakeel Butt , Suren Baghdasaryan , Thomas Gleixner , Toshi Kani , Vishal Moola , Vlastimil Babka , Will Deacon , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, x86@kernel.org X-Mailer: b4 0.16-dev The splitting and merging of kernel page table mappings between small and large is protected by cpa_lock. Commit 5fce67641a3e ("x86/mm/pat: Don't gate cpa_lock on debug_pagealloc_enabled()") disabled gatig of cpa_lock on debug_pagealloc_enabled() to simplify the code presuming that skipping the lock when debug_pagealloc_enabled() was an optimization. However Lorenzo Stoakes notes that: __kernel_map_pages() can be called from irq context: < GFP_ATOMIC context > kfree() or whatever -> ... -> __free_pages_prepare() -> debug_pagealloc_unmap_pages() -> __kernel_map_pages() -> __change_page_attr_set_clr() -> cpa_lock spins [irqs off] So you're spin locking in irq context here, which is probably not a good idea. It would be possible to unconditionally use spin_lock_irqsave() and spin_unlock_irqrestore() but that would complicate locking rules even more. Restore gating of cpa_lock of debug_pagealloc_enabled(), but instead of putting the open-coded condition if (debug_pagealloc_enabled()) before every lock and unlock operation, wrap the condition and the locking operation into cpa_lock() and cpa_unlock() helpers. Signed-off-by: Mike Rapoport (Microsoft) --- arch/x86/mm/pat/set_memory.c | 33 +++++++++++++++++++++++++-------- 1 file changed, 25 insertions(+), 8 deletions(-) diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index b1e780a465b5..4c8922695fd3 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -65,8 +65,25 @@ static const int cpa_warn_level = CPA_PROTECT; * Serialize cpa() using cpa_lock so that we don't allow any other cpu, with * stale large tlb entries, to change the page attribute in parallel to some * other cpu splitting a large page entry along with changing the attribute. + * + * When debug_pagealloc_enabled(), page attributes could be changed in atomic + * context that would warrant disabling IRQs. But since debug_pagealloc always + * uses 4k pages in the direct map there are no races for splits and collapses + * and locking can be just skipped altogether. */ -static DEFINE_SPINLOCK(cpa_lock); +static DEFINE_SPINLOCK(_cpa_lock); + +static inline void cpa_lock(void) +{ + if (!debug_pagealloc_enabled()) + spin_lock(&_cpa_lock); +} + +static inline void cpa_unlock(void) +{ + if (!debug_pagealloc_enabled()) + spin_unlock(&_cpa_lock); +} #define CPA_FLUSHTLB 1 #define CPA_ARRAY 2 @@ -417,7 +434,7 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa) int collapsed = 0; int i; - spin_lock(&cpa_lock); + cpa_lock(); if (cpa->flags & (CPA_PAGES_ARRAY | CPA_ARRAY)) { for (i = 0; i < cpa->numpages; i++) @@ -433,7 +450,7 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa) } if (!collapsed) { - spin_unlock(&cpa_lock); + cpa_unlock(); return; } @@ -444,7 +461,7 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa) pagetable_free(ptdesc); } - spin_unlock(&cpa_lock); + cpa_unlock(); } static void cpa_flush(struct cpa_data *cpa, int cache) @@ -1239,9 +1256,9 @@ static int split_large_page(struct cpa_data *cpa, pte_t *kpte, { struct ptdesc *ptdesc; - spin_unlock(&cpa_lock); + cpa_unlock(); ptdesc = pagetable_alloc(GFP_KERNEL, 0); - spin_lock(&cpa_lock); + cpa_lock(); if (!ptdesc) return -ENOMEM; @@ -2025,9 +2042,9 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int primary) if (cpa->flags & (CPA_ARRAY | CPA_PAGES_ARRAY)) cpa->numpages = 1; - spin_lock(&cpa_lock); + cpa_lock(); ret = __change_page_attr(cpa, primary); - spin_unlock(&cpa_lock); + cpa_unlock(); if (ret) goto out; -- 2.53.0