From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fra-out-015.esa.eu-central-1.outbound.mail-perimeter.amazon.com (fra-out-015.esa.eu-central-1.outbound.mail-perimeter.amazon.com [18.158.153.154]) (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 90C0037A4BD; Wed, 4 Mar 2026 17:13:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=18.158.153.154 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772644393; cv=none; b=TY3zffo0edkgBsQbc6B5BCzU6VBPBB2uXJS0h4JbUMms/Ykt1FONHtqE+05edFUVuOckShoXpty2xBpVyxBB8Ijb7C0rCrIlgZ1RGvNBXs8mM4qoyGN8Qaqc93GKkzqbI9oLJ2Cy4ZS6uiWAFO02s7Rc2L8OBs2z39EH8wZXqwg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772644393; c=relaxed/simple; bh=5/bQ/twgJ+hQHANZmy/rMEaa+DObPC4rHILqYL/5CBk=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=UZ7XxA6ruUC6UXzLhjGWg72PaCKJ/Al+MwL4ldXGjQB8DlCT/ScF/CK8cPQOBreyU0p5zqG6w1Uca/kG5htfkfe5WLabXWGAsCF0azN9fcYJhS9xDe1WXekviy8s+zEwfKhtmAIHmdfTbfA87dfQeOk9ZCPymH+q8cjZzLzaQwo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com; spf=pass smtp.mailfrom=amazon.co.uk; dkim=pass (2048-bit key) header.d=amazon.com header.i=@amazon.com header.b=IG832i3R; arc=none smtp.client-ip=18.158.153.154 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.co.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=amazon.com header.i=@amazon.com header.b="IG832i3R" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazoncorp2; t=1772644391; x=1804180391; h=message-id:date:mime-version:reply-to:subject:to:cc: references:from:in-reply-to:content-transfer-encoding; bh=GOyFbmGrjwCzzxO3kPvRp3gPk09ea9B/RkcYvfV3U7w=; b=IG832i3R7y/mIuqdkP0/6zptYMPPBs+Mx7RXVD/G9E9nSx3KEAAkDpr+ +ffiUX0v88Frbj+JPngjOmuteksVFrnj2aClQsi3LYhkSocB9yO4sRHYW e1M/Eo2S2q7FwG9Ph2Vos1GnLSmdnmgfd48wCT3kaHzdiS+yKZtdOogys iKs2Tapoa+yAuxwo93B0Zl6GIi6KgXL1fjHH7NFYkWJoTAbthVf5PT/Fv dIj5TJdV7gkdiwJjcyOIHCYlo/bVSyCXqdlN8TZ0138byZL2JsdW7gnAU xHvhcMBERVdIOv/zrg08ThRX94hLFYcA8irbZk1+E5FOfysq+Ui5GtYip w==; X-CSE-ConnectionGUID: UYsfpQ/XTKGj1mLFxoxIhw== X-CSE-MsgGUID: vkl+gh6YQl+E7Yf9zukrFQ== X-IronPort-AV: E=Sophos;i="6.21,324,1763424000"; d="scan'208";a="10202501" Received: from ip-10-6-6-97.eu-central-1.compute.internal (HELO smtpout.naws.eu-central-1.prod.farcaster.email.amazon.dev) ([10.6.6.97]) by internal-fra-out-015.esa.eu-central-1.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Mar 2026 17:13:06 +0000 Received: from EX19MTAEUC002.ant.amazon.com [54.240.197.228:21320] by smtpin.naws.eu-central-1.prod.farcaster.email.amazon.dev [10.0.16.189:2525] with esmtp (Farcaster) id 9f0d1b18-a341-4a05-a845-dd316410b6b5; Wed, 4 Mar 2026 17:13:06 +0000 (UTC) X-Farcaster-Flow-ID: 9f0d1b18-a341-4a05-a845-dd316410b6b5 Received: from EX19D005EUB003.ant.amazon.com (10.252.51.31) by EX19MTAEUC002.ant.amazon.com (10.252.51.181) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.37; Wed, 4 Mar 2026 17:13:06 +0000 Received: from [192.168.5.225] (10.106.83.18) by EX19D005EUB003.ant.amazon.com (10.252.51.31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.37; Wed, 4 Mar 2026 17:13:05 +0000 Message-ID: <90cf68db-2e21-4153-8eb6-2c8ffb398d0d@amazon.com> Date: Wed, 4 Mar 2026 17:12:59 +0000 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH RFC 15/17] KVM: guest_memfd: implement userfaultfd missing mode To: Mike Rapoport , CC: Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , James Houghton , "Liam R. Howlett" , "Lorenzo Stoakes" , Michal Hocko , "Muchun Song" , Oscar Salvador , "Paolo Bonzini" , Peter Xu , "Sean Christopherson" , Shuah Khan , "Suren Baghdasaryan" , Vlastimil Babka , , , References: <20260127192936.1250096-1-rppt@kernel.org> <20260127192936.1250096-16-rppt@kernel.org> Content-Language: en-US From: Nikita Kalyazin In-Reply-To: <20260127192936.1250096-16-rppt@kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: EX19D011EUB003.ant.amazon.com (10.252.51.108) To EX19D005EUB003.ant.amazon.com (10.252.51.31) On 27/01/2026 19:29, Mike Rapoport wrote: > From: Nikita Kalyazin > > userfaultfd missing mode allows populating guest memory with the content > supplied by userspace on demand. > > Extend guest_memfd implementation of vm_uffd_ops to support MISSING > mode. > > Signed-off-by: Nikita Kalyazin > Co-developed-by: Mike Rapoport (Microsoft) > Signed-off-by: Mike Rapoport (Microsoft) > --- > virt/kvm/guest_memfd.c | 60 +++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 59 insertions(+), 1 deletion(-) > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 087e7632bf70..14cca057fc0e 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -431,6 +431,14 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf) > ret = VM_FAULT_UFFD_MINOR; > goto out_folio; > } > + > + /* > + * Check if userfaultfd is registered in missing mode. If so, > + * check if a folio exists in the page cache. If not, return > + * VM_FAULT_UFFD_MISSING to trigger the userfaultfd handler. > + */ > + if (userfaultfd_missing(vmf->vma) && IS_ERR_OR_NULL(folio)) > + return VM_FAULT_UFFD_MISSING; > } > > /* folio not in the pagecache, try to allocate */ > @@ -507,9 +515,59 @@ static bool kvm_gmem_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_fla > return true; > } > > +static struct folio *kvm_gmem_folio_alloc(struct vm_area_struct *vma, > + unsigned long addr) > +{ > + struct inode *inode = file_inode(vma->vm_file); > + pgoff_t pgoff = linear_page_index(vma, addr); > + struct mempolicy *mpol; > + struct folio *folio; > + gfp_t gfp; > + > + if (unlikely(pgoff >= (i_size_read(inode) >> PAGE_SHIFT))) > + return NULL; > + > + gfp = mapping_gfp_mask(inode->i_mapping); > + mpol = mpol_shared_policy_lookup(&GMEM_I(inode)->policy, pgoff); > + mpol = mpol ?: get_task_policy(current); > + folio = folio_alloc_mpol(gfp, 0, mpol, pgoff, numa_node_id()); It looks like folio_alloc_mpol_noprof() and filemap_remove_folio() are not actually exported to modules. Would it be ok to export them similar to how it was done in f634f10809ec ("mm/mempolicy: Export memory policy symbols")? diff --git a/mm/filemap.c b/mm/filemap.c index 3e4579e4b8bb..041c7719e524 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -261,6 +261,7 @@ void filemap_remove_folio(struct folio *folio) filemap_free_folio(mapping, folio); } +EXPORT_SYMBOL_FOR_MODULES(filemap_remove_folio, "kvm"); /* * page_cache_delete_batch - delete several folios from page cache diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 3d797d47a040..1dbbbb28a36e 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2442,6 +2442,7 @@ struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order, set_page_refcounted(page); return page_rmappable_folio(page); } +EXPORT_SYMBOL_FOR_MODULES(folio_alloc_mpol_noprof, "kvm"); /** * vma_alloc_folio - Allocate a folio for a VMA. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f634f10809ec3d51d9529dfb0f99bc7cec1b5eff > + mpol_cond_put(mpol); > + > + return folio; > +} > + > +static int kvm_gmem_filemap_add(struct folio *folio, > + struct vm_area_struct *vma, > + unsigned long addr) > +{ > + struct inode *inode = file_inode(vma->vm_file); > + struct address_space *mapping = inode->i_mapping; > + pgoff_t pgoff = linear_page_index(vma, addr); > + int err; > + > + __folio_set_locked(folio); > + err = filemap_add_folio(mapping, folio, pgoff, GFP_KERNEL); > + if (err) { > + folio_unlock(folio); > + return err; > + } > + > + return 0; > +} > + > +static void kvm_gmem_filemap_remove(struct folio *folio, > + struct vm_area_struct *vma) > +{ > + filemap_remove_folio(folio); > + folio_unlock(folio); > +} > + > static const struct vm_uffd_ops kvm_gmem_uffd_ops = { > - .can_userfault = kvm_gmem_can_userfault, > + .can_userfault = kvm_gmem_can_userfault, > .get_folio_noalloc = kvm_gmem_get_folio_noalloc, > + .alloc_folio = kvm_gmem_folio_alloc, > + .filemap_add = kvm_gmem_filemap_add, > + .filemap_remove = kvm_gmem_filemap_remove, > }; > #endif /* CONFIG_USERFAULTFD */ > > -- > 2.51.0 >