From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fra-out-003.esa.eu-central-1.outbound.mail-perimeter.amazon.com (fra-out-003.esa.eu-central-1.outbound.mail-perimeter.amazon.com [3.72.182.33]) (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 715E13BB40; Wed, 4 Mar 2026 17:17:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=3.72.182.33 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772644664; cv=none; b=dh1EkDcnDymr79fu6U7C5a8jQyX4kip8jTmUb38i52YlTUHM17M2qfdjaPz1tf4wAb+xkQH8z/MCAAAIaxiwj95yKap72MfSBu2tpwiPAniIhN7PgESMvfQ1ZQC+xw+fjYDvxGCXgB/4tzG6DY4+fjj++8ftXJuaD1n/y5u6f4E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772644664; c=relaxed/simple; bh=zS2IoNgFK8GIs84v988v1Gkqxk5O7Ci+V3bJWkZ2u/A=; h=Message-ID:Date:MIME-Version:Subject:From:To:CC:References: In-Reply-To:Content-Type; b=CeUJxpVPfmP/h2Pfb5YOWk+oTRTX7hngWVrZMI9tZxQ3iihuXrb9MpZarbbaEek7xo35dMg+ReQtWo1lYpcY0G2zMJ/gCkZ+yRz9eqTVHS5l2T/tdgPyEaIe8sdpVcceZLHqLbDyAmfJhK73nC3ZJRpA3fkXwRc/Klkb7v6I0dI= 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=J0WQJQPq; arc=none smtp.client-ip=3.72.182.33 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="J0WQJQPq" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazoncorp2; t=1772644662; x=1804180662; h=message-id:date:mime-version:reply-to:subject:from:to:cc: references:in-reply-to:content-transfer-encoding; bh=CPgNxadSzjpIoq3NwpOhLARCcrCv7zz8pTRRdyXfzUA=; b=J0WQJQPqEl0uJjsubbOKOEHZ/x1kaN6Uq/wbj2RAGuAQifR6srWYEkvM rWcKhZWdBJYIFFrZTxofYos0fqKR8sjUNCmN37Ca2m1ysijEku1RNniFf Qwb2EprjDfiVHEAY64ez//hVNU1GiDlB8Tb+6HlaxAuON2+z7vCiDt8Y4 23CEpTa9Q99yImA768Ad5OpSWM3oksfKlnI1NhsaeNiR+kA8QDZs9TZ3j aQUdnr6iRn17MvoK+khDgvkg3kHMjWgIAZQsBy+rt9zd8yoHm3iNMXnuk kJldyXbK6w1t2KbsWo4Q/RVIvROorb0gIcxDFeT+tfibdHbsXFzlbblC7 g==; X-CSE-ConnectionGUID: kCX+YtFiRNyIDKqonzWj2Q== X-CSE-MsgGUID: rCpAbOjCT3KIJvBbO/BAqg== X-IronPort-AV: E=Sophos;i="6.21,324,1763424000"; d="scan'208";a="10324163" Received: from ip-10-6-11-83.eu-central-1.compute.internal (HELO smtpout.naws.eu-central-1.prod.farcaster.email.amazon.dev) ([10.6.11.83]) by internal-fra-out-003.esa.eu-central-1.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Mar 2026 17:17:37 +0000 Received: from EX19MTAEUC001.ant.amazon.com [54.240.197.233:10769] by smtpin.naws.eu-central-1.prod.farcaster.email.amazon.dev [10.0.8.50:2525] with esmtp (Farcaster) id 5c685bb8-c81d-4b86-ac12-2b82286bbda5; Wed, 4 Mar 2026 17:17:36 +0000 (UTC) X-Farcaster-Flow-ID: 5c685bb8-c81d-4b86-ac12-2b82286bbda5 Received: from EX19D005EUB003.ant.amazon.com (10.252.51.31) by EX19MTAEUC001.ant.amazon.com (10.252.51.155) 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 17:17:30 +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 17:17:29 +0000 Message-ID: <11b78807-00c3-4131-932c-7e32053f9531@amazon.com> Date: Wed, 4 Mar 2026 17:17:28 +0000 Precedence: bulk X-Mailing-List: linux-kselftest@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 From: Nikita Kalyazin To: Mike Rapoport , CC: Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Baolin Wang , 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 , , , , "david@kernel.org" References: <20260127192936.1250096-1-rppt@kernel.org> <20260127192936.1250096-16-rppt@kernel.org> <90cf68db-2e21-4153-8eb6-2c8ffb398d0d@amazon.com> Content-Language: en-US In-Reply-To: <90cf68db-2e21-4153-8eb6-2c8ffb398d0d@amazon.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: EX19D013EUA004.ant.amazon.com (10.252.50.48) To EX19D005EUB003.ant.amazon.com (10.252.51.31) + David's new email On 04/03/2026 17:12, Nikita Kalyazin wrote: > > > 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 >> >