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 89DD8574091; Mon, 31 Aug 2026 13:48:53 +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=1788184135; cv=none; b=jHUCdi6csgr0D0fOg7gj8j3G2JXfYzRZbpNA9Th+tUdJjz8/UEoaLBkxKG5SZXBdaVgCa4zl5LNb8P4blezFaMmdvH9JzdG0g2S++cOZS7jazON5TmVRR7ZnCLYeqeZ8Z9ZW7lY63fEstKUaOGNvTutXaltDw/+8nN3roxHhlYk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788184135; c=relaxed/simple; bh=Z+qLyLYgglfVAt0jry9Eu1QDTx7t/YHqoOh3IB5+CHU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=RzBevP1X1URqjOzmkHF3ve5dlQuEcRYEy1l6fS2YywJjeMImZlwa8xt41Laq02/GnlMMcB/IIgJGBQIj9Tb7OJH4oUgS/WfkotN+HrFAiVbbsRYE/ahcMCipYc8rZhCqeC55Lt/jvGCr4VsP4VC5MOTrH2FHD/H3iQzSZkmlEmU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=rHQQbFnQ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="rHQQbFnQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E37F01F00A3E; Mon, 31 Aug 2026 13:48:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788184133; bh=3pS4dbfaPcajqzTjq75JwK/8efZslqsTetVbb8BsVt8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=rHQQbFnQXNOOhLwY0MHbEDsz73oDP5cgRrV0XZmK1Rh7ay6r87u2j6tlGsScUfd2k 431vp5EoxgtEF2ni1N1sIfi7rRQycJDIgRdNHTv3w3CyvoRV0aa8E5Q/Kk64/WUcNJ PMo2xdBp7a4I460cZQl8F1D6qOnFK/ZOm6zRC79E= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "David Hildenbrand (Arm)" , Pankaj Gupta , "Lorenzo Stoakes (ARM)" , Sean Christopherson Subject: [PATCH 6.18 40/83] KVM: SEV: Drop FOLL_WRITE for encrypted region registration Date: Mon, 31 Aug 2026 15:34:16 +0200 Message-ID: <20260831133401.558326831@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260831133359.207714926@linuxfoundation.org> References: <20260831133359.207714926@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Pankaj Gupta commit ee1a586dd1fa2f245b3b753a3e44d9263a49240b upstream. When pinning SEV guest memory, drop FOLL_WRITE and rely on FOLL_LONGTERM to break CoW, as *KVM* doesn't actually to the memory using the GUP'd pages. Omitting FOLL_WRITE fixes a regression when using file-backed guest memory that was introduced when KVM (correctly) added FOLL_LONG (e.g. to ensure anonymous memory is migrated out of MIGRATE_CMA/ZONE_MOVABLE before a long term pin). Unfortunately, as of commits: 8ac268436e6d ("mm/gup: disallow FOLL_LONGTERM GUP-nonfast writing to file-backed mappings") a6e79df92e4a ("mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings") GUP uses FOLL_LONGTERM as a canary of sorts to detect pins that are likely to be problematic, and disallows WRITE+LONGTERM pins for file-backed memory. As a result, backing SEV+ guests with file-backed memory, e.g. virtio-pmem, fails due to the disallowed FOLL_LONGTERM+FOLL_WRITE combination. Note, in the past, FOLL_WRITE was required to trigger CoW unsharing, to prevent replacing the page in the (primary MMU's) page tables during a later write fault after already having pinned a (shared) page in MAP_PRIVATE mappings. FOLL_LONGTERM does that nowadays, even without FOLL_WRITE (see gup_must_unshare()). Fixes: 7e066cb9b71a ("KVM: SEV: Use long-term pin when registering encrypted memory regions") Cc: stable@vger.kernel.org Suggested-by: "David Hildenbrand (Arm)" Link: https://lore.kernel.org/all/ad784f05-b36c-4e91-9f17-4c5b826735d0@kernel.org/ Signed-off-by: Pankaj Gupta Acked-by: David Hildenbrand (Arm) Acked-by: Lorenzo Stoakes (ARM) Link: https://patch.msgid.link/20260715063626.65899-1-pankaj.gupta@amd.com [sean: massage changelog, add comment about CoW unsharing] Signed-off-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/svm/sev.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -2727,8 +2727,12 @@ int sev_mem_enc_register_region(struct k if (!region) return -ENOMEM; + /* + * Do NOT specify FOLL_WRITE, as KVM isn't using the pinned pages to + * write memory, and FOLL_LONGTERM itself triggers CoW unshare. + */ region->pages = sev_pin_memory(kvm, range->addr, range->size, ®ion->npages, - FOLL_WRITE | FOLL_LONGTERM); + FOLL_LONGTERM); if (IS_ERR(region->pages)) { ret = PTR_ERR(region->pages); goto e_free;