From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=217.140.110.172 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793628442; b=1PA3Dmc6QXLV/5eWmUAXjOnKdg87B7lpllG2anFbblpPioeppzBwPRg01bqEYEgufYZN yB4oId5+yOkR7WiWFZNYotSy7Xybtp1U9+Qjv2VePvtlIbzo2U/x8nFgrtdgvpdWDgzUE rNMVYIn3KBCMECfT7eetemeiaq/+tI4Bgp4Bgrr+1ngyDNVaHHkUh5aq71mTcZmAeHTfx CB7CvEgdEY7zQCT3DMTfsHNY+ZoH4KEURLFkYL4wHlz7aUu022D8JrcZEmfIXQfbJiWft 2e+2/7+sz6im7x0Bb1eA7SBvamc41QvS4SmLDq78VahVPGF10wsOpydCnGOnuvYOEWg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793628442; h=DMARC-Filter:Received:Received:DKIM-Signature:Date:From:To:Cc: Subject:Message-ID:References:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; bh=XU7NgO7ikkcuAODAla/GTJ/uKE9KKokx9jR+UBm8e9I=; b=G2cI0Llbl2+Z1pd2gjEELYyrSsisETWxtpXv7ATfurERSpr/nkr5LLe2SKk4FasCxQdV DwYiatGtCykN0tCX/jwJLaaKmR/beeeMTnnggjMlOBXbYewms4fPXdjjD3P6F68Y51Ruh lKLYuWiP7ObLtNxW9+uF5Xmk2pMqns/F6cgy9qnVMWeL2iezBfhHmxIAht1C7iNCT/7ga DKSla+JRcpFqWeKR1Le2HmrqzA/ay/+9b71Vv/SHcCbferf9cJIXsKY7wcZ/ACSNXH7CV K0a6SgMmoGZ/3/5esRj3g/kL1aJOSK//q8VJuGNDNu6B/+EbZHWTLR0LvuvGPeQ/+2w== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass header.d=arm.com header.i=@arm.com header.a=rsa-sha256 header.s=foss header.b=jBnJTgXW; arc=none smtp.remote-ip=217.140.110.172 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 87CE6606A33B for ; Mon, 2 Nov 2026 14:07:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 87CE6606A33B Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=arm.com header.i=@arm.com header.a=rsa-sha256 header.s=foss header.b=jBnJTgXW Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 688DD1691; Mon, 2 Nov 2026 06:07:17 -0800 (PST) Received: from e129823.arm.com (e129823.arm.com [10.2.213.3]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8799A3F59E; Mon, 2 Nov 2026 06:07:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1793628440; bh=okA/++pW27xIdWmqVZy2ykipgObAMuboinr6ec1sU5Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jBnJTgXWfHg+QNg7DQOItwTLd4XyLxdbeDwlTbO7ufrAlk2WRjxuW02nKMvY37PPk QL0RxH1OvafU8aG9fX+0TV5TunRW15831s/wOJZNZVYvdCkmiqkmIFDuopKtGau0G/ +lMCckX1nd4n1qkrQi9h+UUvCfMyPVH/6hwSKrnU= Date: Mon, 2 Nov 2026 14:07:16 +0000 From: Yeoreum Yun To: "David Hildenbrand (Arm)" Cc: Yeoreum Yun , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lorenzo Stoakes , Jason Gunthorpe , John Hubbard , Peter Xu , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Andrew Morton , Rik van Riel , Yuan-Hao Hsu Subject: Re: [PATCH v2 2/4] mm: internal: fix inconsistent in folio_pte_batch_flags() for shadow stack Message-ID: References: <20261102-refactor_gup_fast-v2-0-bc1ac018c834@arm.com> <20261102-refactor_gup_fast-v2-2-bc1ac018c834@arm.com> <85c4a87b-2c8b-4ef5-bb30-6518080f8be0@kernel.org> <9a67e7f6-0ec6-414d-8689-c70eeed6100c@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9a67e7f6-0ec6-414d-8689-c70eeed6100c@kernel.org> > >>> + if (unlikely((flags & (FPB_RESPECT_WRITE | FPB_RESPECT_DIRTY)) == FPB_RESPECT_WRITE && > >>> + writable != !!pte_write(pte))) > >> > >> It might be nicer and more efficient to track if any was readonly/not-writable and > >> > >> any_unwritable = !pte_write(pte); > >> > >> And checking once after the loop. > > > > Sorry. But I couldn't follow. If we accumalate with any_unwritable > > and check it out of loop once only, we couldn't properly nr value or > > Am I missing something? > > Ah. The idea was to simply reject the batch entirely if that happens. It would > only matter if some folio PTEs are writable while others are not ... well, ok, > there are some cases where that can happen, but it's not really the common case. > > I think we should simply disallow ever getting large folios into shadow stack > VMAs for now. So I'd prefer the fix below. > > Thoughts? That's my preference too and we've discussed :) I'll repost with below unless anyone has any strong comment. > > >> > >> diff --git a/mm/khugepaged.c b/mm/khugepaged.c > >> index 4b71d010b2aff..9a2dc90ef9690 100644 > >> --- a/mm/khugepaged.c > >> +++ b/mm/khugepaged.c > >> @@ -367,6 +367,9 @@ int hugepage_madvise(struct vm_area_struct *vma, > >> { > >> switch (advice) { > >> case MADV_HUGEPAGE: > >> + /* PTE batching doesn't work reliably. */ > >> + if (vma_test_single_mask(vma, VMA_SHADOW_STACK)) > >> + break; > >> *vm_flags &= ~VM_NOHUGEPAGE; > >> *vm_flags |= VM_HUGEPAGE; > >> break; > >> > > > > Yeap. once we do this, we don't need to this fix patch anyway. > > But I don't know whether there is practical case changing the > > VMA_SHADOW_STACK with huge though it is initailised with NOHUGE. > > > > -- > Cheers, > > David -- Sincerely, Yeoreum Yun