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 C9EBC3750DB; Wed, 1 Jul 2026 16:39:09 +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=1782923951; cv=none; b=Ka4/NkhUSdEwREgGAHVPWUsp31LcBcMggR1E0pqRVljcUXPq3zoCLoMZPrK6f8FF9lp4vN2PxZqInJZI0aVAMv2HNXaX5RzzLGZ+1NX4H6NrJZeQ46rZqpZTYQ+RiX+cgGRtQnfYge/ol3KONjj3b/JS2G4T2gvmW32KSK27AEk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782923951; c=relaxed/simple; bh=mTLpAMVMzHCWtZWJCRnhXqV2f49vXr3MZyHU/ofR0vU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=OnhxjsnKAcT7u3RwlWeHlLpdEyzEEwDzgrvG7tAfnhxFyplzOrLSY2Vv8YJkPsxFhSbb0CpMvMGoB2J8t5mmifo0InA54Fil0C2SwKr+ImnO7/IlOjYpHjEIWcqTK4LcL8x88NBMHnbz7Gbrdfty1WnO4qyH6wF3IZjYSx4a224= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WZlT1uM3; 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="WZlT1uM3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 189D21F000E9; Wed, 1 Jul 2026 16:39:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782923949; bh=rFi7za6TMIBXh1ci1ZaV/CadCFF1+ZDP7ntbr0l7lLY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=WZlT1uM3Cq+PDML6CkOmUj7mo97tNFxZP6HbxcHpAqhes7scZkbIPp0D4tbK5mEGv BGs6DmxNwmtpzjc+Db9fe9RA7xcpaPec+dqMhRmst7RG97GcBbE93y3iQdBlcuxnqC h2JT/WvFiF141jwwC5wpI4g1LpFKBTYtoVxGX2lyCgQAyjku/e96afZ7fyc07iEWJd vXSESozov16GQVICdGUOxfTmcAYhvOkqD/IUR4VCEOvmrLY+x0oRRoI9H/1WSmcBZB H6sb2CcAVFi+PPgrIdGfWyyY6w+SboHdsMcE2Sjd/OCGVPbTPxnc1NsYJ3CFl62tK6 CaPldLmm+HrMQ== Message-ID: Date: Wed, 1 Jul 2026 18:39:04 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] KVM: SEV: drop FOLL_LONGTERM for encrypted region registration To: Sean Christopherson Cc: Pankaj Gupta , pbonzini@redhat.com, tglx@kernel.org, mingo@redhat.com, dave.hansen@linux.intel.com, bp@alien8.de, x86@kernel.org, thomas.lendacky@amd.com, hpa@zytor.com, yangge1116@126.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260701144543.39582-1-pankaj.gupta@amd.com> <1cc159b9-5f94-4524-8e03-efe91601ccfc@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/1/26 18:30, Sean Christopherson wrote: > On Wed, Jul 01, 2026, David Hildenbrand (Arm) wrote: >> On 7/1/26 16:45, Pankaj Gupta wrote: >>> commit 7e066cb9b71a ("KVM: SEV: Use long-term pin when registering encrypted memory regions") >>> added FOLL_LONGTERM to sev_mem_enc_register_region() so anonymous guest RAM is >>> migrated out of MIGRATE_CMA/ZONE_MOVABLE before a long term pin. This breaks >>> virtio-pmem which has file backed (MAP_SHARED) host mapping where GUP rejects >>> FOLL_WRITE | FOLL_LONGTERM since: >>> >>> commit 8ac268436e6d ("mm/gup: disallow FOLL_LONGTERM GUP-nonfast writing to file-backed mappings") >>> commit a6e79df92e4a ("mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings"). >>> >>> Drop FOLL_LONGTERM when registering encrypted memory regions and restore >>> the previous behavior. >> >> But that breaks the original issue of breaking ZONE_MOVABLE/CMA? > > Ya. > >> If it is a longterm pin, it must use FOLL_LONGTERM. :/ > > Heh, well, KVM showed that that's not entirely true for many years :-) What exactly do you mean? KVM MMUs sync through memory notifiers and doesn't need this. It's only our "interesting" CoCo code :) > > Assuming we can't solve this some other way, and that there are "real" use cases > that were broken by adding FOLL_LONGTERM, maybe this as a hack-a-fix? Well, it's not a driver's decision to make. :P But, can we actually whitelist virtio-pmem in GUP code somehow? I mean, it does not suffer from the documented writeback issue, that we wanted to protect from. We similarly allow shmem and hugetlb there. -- Cheers, David