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 5F25348F02C for ; Mon, 21 Sep 2026 12:03:14 +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=1789992195; cv=none; b=YmrfQpfml4dGRCHhPPXwYAmjI6vKEWjUoWJZRP6BEYOXfEUZ3hVQe4C9pyEu3VqhBVDU42TzhQW0fLe2Fgch2zQZaF3km+bwHPOtmoGEiaU3RDqqXq0hWhKyl8shBaK/B/ZcUjLrE7D5WKj3WVt1o5rQqBBjTJUxQ3UOnO+YZ/g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789992195; c=relaxed/simple; bh=UPEx1+0PEEqGCPL4zYv4gTCRpfm7n9hAyx6GaM1Wyvk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ff4Xp9mAa9CH7479WtpRxQ/NKkRoifhYyikMmRuoMkIJII9MZtLfy5pqw4TY5P04oFgF5TgSzZS/Nx09mCC/kcV83M9It05xbOxP2wCX68pCf93No2agi1W11ZJHiW/T/L7ej5tURXuzhcli+FYOLWgcYdihvmmndlg6n9RdS4Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=W2SadKpx; 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="W2SadKpx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AE8F71F000FF; Mon, 21 Sep 2026 12:03:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789992194; bh=Mpg5926h34Bs19sqds9l3xd0hZ+AgGPbZWYnHshxVF0=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=W2SadKpxtPg29h2QNCnTPsl4SyrVbj7D+Oz6AkVxLdbBLix4P5XrDQ1/61SoZRycf cnkBq1ZwvbvdlX5wpHNvZjPpMfyJr0V4rsxAatZ3WtDtnfbEvoSiDL9Td28tFOW82f 5IRbih1CL6ciudCmxnorWvNWE80UjyKsJ7C2NRK3M/7lV17UZ2xbQA7vIrOye76trs ObdP2NiHPtrqHIvg4KNlfJ8TPEci1JH+iqHdyCJE82LDVmoZBpigwqgpzMbSe0x74J 5yDB8pmtBsOEfcgdLWLYyYahKovtwECZQiQMEqIuU0AIpJej4d2qdyMCVuV6nGqh39 UzMV0z0hV23NQ== Date: Mon, 21 Sep 2026 13:03:07 +0100 From: "Lorenzo Stoakes (ARM)" To: Lance Yang Cc: akpm@linux-foundation.org, david@kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, usama.arif@linux.dev, kas@kernel.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/1] mm: disallow raw PFN mappings of huge/shared zeropage Message-ID: References: <20260921054225.28537-1-lance.yang@linux.dev> 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=us-ascii Content-Disposition: inline In-Reply-To: <20260921054225.28537-1-lance.yang@linux.dev> On Mon, Sep 21, 2026 at 01:42:25PM +0800, Lance Yang wrote: > From: Lance Yang > > Handling the huge/shared zeropage correctly in vmf_insert_pfn_pmd() and > vmf_insert_pfn_prot() is more involved. We would need to check whether the > VMA allows it and keep the mapping read-only, similar to the checks in > vm_mixed_ok(). > > No in-tree user needs that support, so reject these mappings with > VM_FAULT_SIGBUS rather than complicate the code for now. > > Link: https://lore.kernel.org/all/20260917121010.60966-1-lance.yang@linux.dev/ > Suggested-by: Kiryl Shutsemau (Meta) > Suggested-by: David Hildenbrand (Arm) > Reviewed-by: Kiryl Shutsemau (Meta) > Signed-off-by: Lance Yang Seems sensible to me! Reviewed-by: Lorenzo Stoakes (ARM) > --- > v1 -> v2: > - Reject the shared zeropage in vmf_insert_pfn_prot() (per Kiryl) - thanks! > - Explain the VMA validation and read-only requirements (per David) - thanks! > - Pick up Kiryl's Reviewed-by tag. > - https://lore.kernel.org/all/20260917121010.60966-1-lance.yang@linux.dev/ > > mm/huge_memory.c | 3 +++ > mm/memory.c | 3 +++ > 2 files changed, 6 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 8aa2daba3739..1d4fe4452c98 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1728,6 +1728,9 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, unsigned long pfn, > (VM_PFNMAP|VM_MIXEDMAP)); > BUG_ON((vma->vm_flags & VM_PFNMAP) && vma_is_cow_mapping(vma)); > > + if (unlikely(is_huge_zero_pfn(pfn))) > + return VM_FAULT_SIGBUS; > + > pfnmap_setup_cachemode_pfn(pfn, &pgprot); > > return insert_pmd(vma, addr, vmf->pmd, fop, pgprot, write); > diff --git a/mm/memory.c b/mm/memory.c > index 926276d41920..7d821b110df0 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2860,6 +2860,9 @@ vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr, > BUG_ON((vma->vm_flags & VM_PFNMAP) && vma_is_cow_mapping(vma)); > BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn)); > > + if (unlikely(is_zero_pfn(pfn))) > + return VM_FAULT_SIGBUS; > + > if (addr < vma->vm_start || addr >= vma->vm_end) > return VM_FAULT_SIGBUS; > > -- > 2.49.0 -- Cheers, Lorenzo