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 D2B0037997E; Mon, 15 Jun 2026 18:35:32 +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=1781548533; cv=none; b=WPa6+QlaqzxEJAyYUUc1jBHzpQCKgdoaub40vArj4gHN3t8XUPkJLaL3anlyQptgGK+KAP0xC7k4BGzwv97f5oMcQLWAPMvpO8vNveL1sG6skB7w1djDhStZ66ym/dcVumIP4bKOO1k1xYwbyY1Jd9JzAWOuxArMVJ2e3BVr5+w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781548533; c=relaxed/simple; bh=2h3R1KaG6R0309+dcpm2CGuj1MxQ+ME+WvA5c8KJVg8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=dWn3srSRNCZ2zMlPS8EKYpr1zGbE26Iyh5zoT9WkAT8b0ppY33fIyFlJt9gfnruwgmF9EXFaDI0xlJ/jh7tbSjT4S90l4XB6DcIHi90PkZtEXD2VFRJ6fmud69p0AVjRZ4c1LhtF34S855+oiSH7KsUkjFMusBf/exO9hN+9dKo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jlAQG2xW; 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="jlAQG2xW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0454D1F000E9; Mon, 15 Jun 2026 18:35:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781548532; bh=hzUbXfgg1+bBubgu8gN+hwknySP5HOytcelW2HhsCuA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=jlAQG2xWMZDdf/TzVptw6qaxuKXJK92zOL3nTKtS7cwaic2k+bAq+ARNG9AezSHH8 IS2fSOS9S07JnquBqBhgmdo1FGtmTkV03sgRuB22ATBYrEUyqqpgrtp0fJtk8HPhKm ulaxvPNAnX2dXPwAwr5kpilaGWvIcjWK0OHquB/CUSlk0p48wTWjRmQ+86zfYQDoCm Xluit6eChkKE3LPRx7VyEw/d81L+RRLbRF9jTEfjOBTKi6jkh0TPFTM7b5CFMX1Z13 DDysW8JKdDtafNe5Ay8+LAeF94jqSNCVoSw63n3Wa7CQBIuWYFQ5vYM4PEvYd4rw1J FPUWgIJy6t6mA== Message-ID: <1f74f3b9-fda5-40e1-9170-5861ebac9ca8@kernel.org> Date: Mon, 15 Jun 2026 20:35:21 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 2/3] KVM: guest_memfd: support folio migration for non-confidential VMs To: Shivank Garg , "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Paolo Bonzini , Shuah Khan , Chao Peng , Nikunj A Dadhania , Ira Weiny , Michael Roth , Pankaj Gupta , Ackerley Tng , Fuad Tabba , Sean Christopherson , Vishal Annapurve , Nikita Kalyazin , Patrick Roy , Pratik Sampat , Ashish Kalra Cc: linux-fsdevel@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20260611-shivank-gmem-migrate-v1-0-2d266bfc6f95@amd.com> <20260611-shivank-gmem-migrate-v1-2-2d266bfc6f95@amd.com> 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 6/11/26 15:05, Shivank Garg wrote: > guest_memfd folios are currently marked unmmovable, so the kernel > cannot perform NUMA-balancing, memory compaction, etc. > This is unavoidable for confidential VMs (SEV-SNP, TDX), > since memory is encrypted and copying it need firmware assistance. > However, for non-cofidential VMs (like firecracker), we can migrate > the folios. > > Mark non-confidential VMs as movable and implement > kvm_gmem_migrate_folio() using filemap_migrate_folio(). > > This lays the ground work for migrating cofidential guest_memfd > later. Once the firmware-assisted copying support is available, > those VMs can be made movable. The confidential folio content can > be copied separately, and the destination folio can be marked with > FOLIO_CONTENT_COPIED so __migrate_folio() skips the host-side > folio_mc_copy(). > > Signed-off-by: Shivank Garg > --- > virt/kvm/guest_memfd.c | 50 +++++++++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 45 insertions(+), 5 deletions(-) > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 806a42f0e031a1c7729f53c786316d2502532553..e4470106fc7792f328bce5275419683328c8b4ab 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -487,13 +487,45 @@ static struct file_operations kvm_gmem_fops = { > .fallocate = kvm_gmem_fallocate, > }; > > +#ifdef CONFIG_MIGRATION > static int kvm_gmem_migrate_folio(struct address_space *mapping, > struct folio *dst, struct folio *src, > enum migrate_mode mode) > { > - WARN_ON_ONCE(1); > - return -EINVAL; > + struct inode *inode = mapping->host; > + pgoff_t start, end; > + int ret; > + > + if (!filemap_invalidate_trylock_shared(mapping)) > + return -EAGAIN; > + > + start = src->index; > + end = start + folio_nr_pages(src); > + > + kvm_gmem_invalidate_begin(inode, start, end); > + > + /* > + * For non-confidential guest_memfd the folio is host-readable, > + * so filemap_migrate_folio() can copy the contents itself via > + * folio_mc_copy(). > + * > + * This is also the hook point for confidential VMs (SEV-SNP, TDX) once > + * they are made movable: the host cannot copy encrypted/private memory, > + * so a firmware-assisted copy would run here. > + * Idea: https://lore.kernel.org/r/20260428155043.39251-8-shivankg@amd.com > + * Mark the @dst->migrate_info field with FOLIO_CONTENT_COPIED, so > + * __migrate_folio() skip folio_mc_copy() for confidential VMs. > + */ > + ret = filemap_migrate_folio(mapping, dst, src, mode); > + > + kvm_gmem_invalidate_end(inode, start, end); > + > + filemap_invalidate_unlock_shared(mapping); > + return ret; > } > +#else > +#define kvm_gmem_migrate_folio NULL > +#endif > > static int kvm_gmem_error_folio(struct address_space *mapping, struct folio *folio) > { > @@ -592,9 +624,17 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) > inode->i_size = size; > mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); > mapping_set_inaccessible(inode->i_mapping); > - mapping_set_unmovable(inode->i_mapping); > - /* Unmovable mappings are supposed to be marked unevictable as well. */ > - WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); > + > + /* > + * Confidential VMs (SEV-SNP, TDX) bind encryption to the physical > + * address and require firmware assisted copy, so their folios cannot > + * be migrated yet. > + */ > + if (kvm_arch_has_private_mem(kvm)) { > + mapping_set_unmovable(inode->i_mapping); > + /* Unmovable mappings are supposed to be marked unevictable as well. */ > + WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); We would still want our movable mappings to be flagged unevictable. > + } > As discussed, for guest_memfd instances that support page migration, we would want to also allocate the pages in for guest_memfd as GFP_HIGHUSER_MOVABLE. That is, handle the mapping_set_gfp_mask() call as well. It will unlock access to areas reserved for movable allocations (CMA/ ZONE_MOVABLE) and properly let the page allocator group pages by mobility (MOVABLE vs. UNMOVABLE vs. RECLAIMABLE). -- Cheers, David