From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 5D69038423B; Tue, 28 Apr 2026 23:25:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777418717; cv=none; b=G1pRTC0MqHSxchSjuDEyKKkTjdsmyySubzd3SXNX0kuPHb82lORyh/S742a28dPkuESL/2ow1kQ4MgAqDPm+02BqeEfEKIrLVSF8YoAPqruE28agO2KJS33hdQWyx/9vI2W9inC/a/Ces4phn8KodfoDI8J3zkmnS8InUQIgmZQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777418717; c=relaxed/simple; bh=svzUpBBdu7c/okzZHdk95phkHOtm8MccWFmUfZ97Ar8=; h=From:Subject:Date:Message-Id:MIME-Version:Content-Type:To:Cc; b=O6Folxw3Z8l4WHGDwI7xItLj022vih4PQoFMkrWY4w9FQkeImDU2H9ylFMVTwjVbypJwO3Gq/MhRC29IDvjASYUSE2YJU8kDKCI2KUjNQZreVorcOxzukn/GkSEq6eocdqSatbCEYqMjCSHZF2vANoI6MYalCkNZtJjoLInE+x4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NWJCOnWz; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NWJCOnWz" Received: by smtp.kernel.org (Postfix) with ESMTPS id 0C003C2BCB3; Tue, 28 Apr 2026 23:25:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777418717; bh=svzUpBBdu7c/okzZHdk95phkHOtm8MccWFmUfZ97Ar8=; h=From:Subject:Date:To:Cc:Reply-To:From; b=NWJCOnWz9Zy+sGJdjfmd774CXIoDYgCTLGSnXlNfv5ATQgY1Px/iGnL/KHuvEtcDh YEMsfwXEdj7jttG0RadnWi+LJtM2pvoGMQTZGeM5J5Z/2JWskBZjf4456sWeBUg+qg +StYFMY+99PHUVyVTuTRAqARQMfD+FXl86nv4R1w+QZ2Y/s0F8ckQM8cNWSCDkLRNX fFACHTFAOEjpllyutxJabZo/zrNqaITV+Zy4DdD/kkJJ52l2+tyYsxnNKTK9c4/uYq Pn+SbUJQoI42nUkBh4hl5g8J3Gr+n9On2fyZ1/A9Hz3XG9WXyepnmNbklMaB4DZ2km UaL6BDF3iCKSQ== Received: from aws-us-west-2-korg-lkml-1.web.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.lore.kernel.org (Postfix) with ESMTP id E6C46FF8875; Tue, 28 Apr 2026 23:25:16 +0000 (UTC) From: Ackerley Tng via B4 Relay Subject: [PATCH RFC v5 00/53] guest_memfd: In-place conversion support Date: Tue, 28 Apr 2026 16:24:55 -0700 Message-Id: <20260428-gmem-inplace-conversion-v5-0-d8608ccfca22@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-B4-Tracking: v=1; b=H4sIAMdB8WkC/3WOsQ7CIBRFf6VhFqUg1jqZmPgBrsaBwqMlttBAQ 2pM/13KpIPjfbnn3PdGAbyBgE7FG3mIJhhnU+CbAslO2BawUSkjSuiBUMpxO8CAjR17IQFLZyP 4lcGNIqpRrK44EyjRowdt5my+o9v1gh7p2IgAuPHCym6VPuOwszBPa78zYXL+lR+JLFN5k5Xs7 2ZkmGCuZUlFRUAe63PrXNvDVroh78X9l4ge/ov2SQSppqHmRGv1I1qW5QNanisVKAEAAA== X-Change-ID: 20260225-gmem-inplace-conversion-bd0dbd39753a To: aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, david@kernel.org, ira.weiny@intel.com, jmattson@google.com, jthoughton@google.com, michael.roth@amd.com, oupton@kernel.org, pankaj.gupta@amd.com, qperret@google.com, rick.p.edgecombe@intel.com, rientjes@google.com, shivankg@amd.com, steven.price@arm.com, tabba@google.com, willy@infradead.org, wyihan@google.com, yan.y.zhao@intel.com, forkloop@google.com, pratyush@kernel.org, suzuki.poulose@arm.com, aneesh.kumar@kernel.org, Paolo Bonzini , Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Baoquan He , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Jason Gunthorpe , Vlastimil Babka Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, Ackerley Tng X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1777418714; l=12535; i=ackerleytng@google.com; s=20260225; h=from:subject:message-id; bh=svzUpBBdu7c/okzZHdk95phkHOtm8MccWFmUfZ97Ar8=; b=0QkV8hZP8hOH+hNCjeSswDYv3vwtP0XxQooAEB0MYPOPaJ61NRztWoDddvIp3XyKA8ztoEmSN kkCot+LkiE4DyIM4Rvv4GTzuOq5tFyFCn3jEr0j4bB0zWVpIPJWfHca X-Developer-Key: i=ackerleytng@google.com; a=ed25519; pk=sAZDYXdm6Iz8FHitpHeFlCMXwabodTm7p8/3/8xUxuU= X-Endpoint-Received: by B4 Relay for ackerleytng@google.com/20260225 with auth_id=649 X-Original-From: Ackerley Tng Reply-To: ackerleytng@google.com This is RFC v5 of guest_memfd in-place conversion support. Up till now, guest_memfd supports the entire inode worth of memory being used as all-shared, or all-private. CoCo VMs may request guest memory to be converted between private and shared states, and the only way to support that currently would be to have the userspace VMM provide two sources of backing memory from completely different areas of physical memory. pKVM has a use case for in-place sharing: the guest and host may be cooperating on given data, and pKVM doesn't protect data through encryption, so copying that given data between different areas of physical memory as part of conversions would be unnecessary work. This series also serves as a foundation for guest_memfd huge page support. Now, guest_memfd only supports PAGE_SIZE pages, so if two sources of backing memory are used, the userspace VMM could maintain a steady total memory utilized by punching out the pages that are not used. When huge pages are available in guest_memfd, even if the backing memory source supports hole punching within a huge page, punching out pages to maintain the total memory utilized by a VM would be introducing lots of fragmentation. In-place conversion avoids fragmentation by allowing the same physical memory to be used for both shared and private memory, with guest_memfd tracks the shared/private status of all the pages at a per-page granularity. The central principle, which guest_memfd continues to uphold, is that any guest-private page will not be mappable to host userspace. All pages will be mmap()-able in host userspace, but accesses to guest-private pages (as tracked by guest_memfd) will result in a SIGBUS. This series introduces a guest_memfd ioctl (not kvm, vm or vcpu, but guest_memfd ioctl) that allows userspace to set memory attributes (shared/private) directly through the guest_memfd. This is the appropriate interface because shared/private-ness is a property of memory and hence the request should be sent directly to the memory provider - guest_memfd. Tested with both CONFIG_KVM_VM_MEMORY_ATTRIBUTES enabled and disabled: + tools/testing/selftests/kvm/guest_memfd_test.c + tools/testing/selftests/kvm/pre_fault_memory_test.c + tools/testing/selftests/kvm/x86/guest_memfd_conversions_test.c + tools/testing/selftests/kvm/x86/private_mem_conversions_test.c + tools/testing/selftests/kvm/x86/private_mem_conversions_test.sh + tools/testing/selftests/kvm/x86/private_mem_kvm_exits_test.c Updates for this revision: + For TDX and SNP, PRESERVE supported only before VM is finalized only for to_private conversions. + This allows PRESERVE to be used as part of the VM memory loading/encryption flow + Only support PRESERVE for to_private conversions (to_shared on populated memory on TDX would cause zeroing) + Relaxed constraints for SNP and TDX to allow NULL to be passed as source address. + Dropped KVM_CAP_MEMORY_ATTRIBUTES2. KVM_CAP_MEMORY_ATTRIBUTES reports attributes supported by the KVM_SET_MEMORY_ATTRIBUTES VM ioctl, and KVM_CAP_GUEST_MEMFD_MEMORY_ATTRIBUTES reports attributes supported bt the KVM_SET_MEMORY_ATTRIBUTES2 guest_memfd ioctl. + KVM_SET_MEMORY_ATTRIBUTES2 is not supported by the VM ioctl + Resolve locking issue when kvm_gmem_get_attribute() is called from kvm_mmu_zap_collapsible_spte() by bugging the VM. guest_memfd memslots don't support dirty tracking, so the locking issue is not on an accessible code path. + Moved guest_memfd_conversions_test.c to only be compiled and tested for x86, since it depends so heavily on KVM_X86_SW_PROTECTED_VM's as a testing vehicle TODOs + Perhaps further clarify PRESERVE flag: [8] + Resolve issue where guest_memfd_conversions_test, which uses the kselftest framework, doesn't perform teardown on assertion failure. Please see proposal at [9] + Test with TDX selftests. We're in the process of rebasing TDX selftests on this series and will post updates when that's tested. I would like feedback on: + Content modes: 0 (MODE_UNSPECIFIED), ZERO, and PRESERVE. Is that all good, or does anyone think there is a use case for something else? + Should the content modes apply even if no attribute changes are required? + See notes added in "KVM: guest_memfd: Apply content modes while setting memory attributes" + Possibly related: should setting attributes be allowed if some sub-range requested already has the requested attribute? + Structure of how various content modes are checked for support or applied? I used overridable weak functions for architectures that haven't defined support, and defined overrides for x86 to show how I think it would work. For CoCo platforms, I only implemented TDX for illustration purposes and might need help with the other platforms. Should I have used kvm_x86_ops? I tried and found myself defining lots of boilerplate. + The use of private_mem_conversions_test.sh to run different options in private_mem_conversions_test. If this makes sense, I'll adjust the Makefile to have private_mem_conversions_test tested only via the script. This series is based on kvm/next, and here's the tree for your convenience: https://github.com/googleprodkernel/linux-cc/commits/guest_memfd-inplace-conversion-v5 Older series: + RFCv4 is at [7] + RFCv3 is at [6] + RFCv2 is at [5] + RFCv1 is at [4] + Previous versions of this feature, part of other series, are available at [1][2][3]. [1] https://lore.kernel.org/all/bd163de3118b626d1005aa88e71ef2fb72f0be0f.1726009989.git.ackerleytng@google.com/ [2] https://lore.kernel.org/all/20250117163001.2326672-6-tabba@google.com/ [3] https://lore.kernel.org/all/b784326e9ccae6a08388f1bf39db70a2204bdc51.1747264138.git.ackerleytng@google.com/ [4] https://lore.kernel.org/all/cover.1760731772.git.ackerleytng@google.com/T/ [5] https://lore.kernel.org/all/cover.1770071243.git.ackerleytng@google.com/T/ [6] https://lore.kernel.org/r/20260313-gmem-inplace-conversion-v3-0-5fc12a70ec89@google.com/T/ [7] https://lore.kernel.org/all/20260326-gmem-inplace-conversion-v4-0-e202fe950ffd@google.com/T/ [8] https://lore.kernel.org/all/CAEvNRgGbMhkX310CkFY_M5x-zod=BDTiuznrZ0XvFPUK7weL1A@mail.gmail.com/ [9] https://lore.kernel.org/all/20260414-selftest-global-metadata-v1-0-fd223922bc57@google.com/T/ Signed-off-by: Ackerley Tng --- Ackerley Tng (34): KVM: x86/mmu: Bug the VM if gmem attributes are queried to determine max mapping level KVM: guest_memfd: Update kvm_gmem_populate() to use gmem attributes KVM: guest_memfd: Only prepare folios for private pages KVM: Move kvm_supported_mem_attributes() to kvm_host.h KVM: guest_memfd: Add basic support for KVM_SET_MEMORY_ATTRIBUTES2 KVM: guest_memfd: Ensure pages are not in use before conversion KVM: guest_memfd: Call arch invalidate hooks on conversion KVM: guest_memfd: Return early if range already has requested attributes KVM: guest_memfd: Advertise KVM_SET_MEMORY_ATTRIBUTES2 ioctl KVM: guest_memfd: Handle lru_add fbatch refcounts during conversion safety check KVM: guest_memfd: Use actual size for invalidation in kvm_gmem_release() KVM: guest_memfd: Determine invalidation filter from memory attributes KVM: guest_memfd: Introduce default handlers for content modes KVM: guest_memfd: Apply content modes while setting memory attributes KVM: x86: Support SW_PROTECTED_VM in applying content modes KVM: TDX: Make source page optional for KVM_TDX_INIT_MEM_REGION KVM: x86: Support SNP and TDX applying content modes KVM: x86: Bug CoCo VM on page fault before finalizing KVM: Add CAP to enumerate supported SET_MEMORY_ATTRIBUTES2 flags KVM: selftests: Test basic single-page conversion flow KVM: selftests: Test conversion flow when INIT_SHARED KVM: selftests: Test conversion precision in guest_memfd KVM: selftests: Test conversion before allocation KVM: selftests: Convert with allocated folios in different layouts KVM: selftests: Test that truncation does not change shared/private status KVM: selftests: Test conversion with elevated page refcount KVM: selftests: Test that conversion to private does not support ZERO KVM: selftests: Support checking that data not equal expected KVM: selftests: Test that not specifying a conversion flag scrambles memory contents KVM: selftests: Reset shared memory after hole-punching KVM: selftests: Provide function to look up guest_memfd details from gpa KVM: selftests: Make TEST_EXPECT_SIGBUS thread-safe KVM: selftests: Update private_mem_conversions_test to mmap() guest_memfd KVM: selftests: Add script to exercise private_mem_conversions_test Michael Roth (1): KVM: SEV: Make 'uaddr' parameter optional for KVM_SEV_SNP_LAUNCH_UPDATE Sean Christopherson (18): KVM: guest_memfd: Introduce per-gmem attributes, use to guard user mappings KVM: Rename KVM_GENERIC_MEMORY_ATTRIBUTES to KVM_VM_MEMORY_ATTRIBUTES KVM: Enumerate support for PRIVATE memory iff kvm_arch_has_private_mem is defined KVM: Stub in ability to disable per-VM memory attribute tracking KVM: guest_memfd: Wire up kvm_get_memory_attributes() to per-gmem attributes KVM: Move KVM_VM_MEMORY_ATTRIBUTES config definition to x86 KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes KVM: guest_memfd: Enable INIT_SHARED on guest_memfd for x86 Coco VMs KVM: selftests: Create gmem fd before "regular" fd when adding memslot KVM: selftests: Rename guest_memfd{,_offset} to gmem_{fd,offset} KVM: selftests: Add support for mmap() on guest_memfd in core library KVM: selftests: Add selftests global for guest memory attributes capability KVM: selftests: Add helpers for calling ioctls on guest_memfd KVM: selftests: Test that shared/private status is consistent across processes KVM: selftests: Provide common function to set memory attributes KVM: selftests: Check fd/flags provided to mmap() when setting up memslot KVM: selftests: Update pre-fault test to work with per-guest_memfd attributes KVM: selftests: Update private memory exits test to work with per-gmem attributes Documentation/virt/kvm/api.rst | 139 ++++- .../virt/kvm/x86/amd-memory-encryption.rst | 19 +- Documentation/virt/kvm/x86/intel-tdx.rst | 4 + arch/x86/include/asm/kvm_host.h | 2 +- arch/x86/kvm/Kconfig | 15 +- arch/x86/kvm/mmu/mmu.c | 20 +- arch/x86/kvm/svm/sev.c | 18 +- arch/x86/kvm/vmx/tdx.c | 8 +- arch/x86/kvm/x86.c | 145 ++++- include/linux/kvm_host.h | 74 ++- include/trace/events/kvm.h | 4 +- include/uapi/linux/kvm.h | 21 + mm/swap.c | 2 + tools/testing/selftests/kvm/Makefile.kvm | 5 + tools/testing/selftests/kvm/include/kvm_util.h | 141 ++++- tools/testing/selftests/kvm/include/test_util.h | 34 +- .../selftests/kvm/kvm_has_gmem_attributes.c | 17 + tools/testing/selftests/kvm/lib/kvm_util.c | 130 +++-- tools/testing/selftests/kvm/lib/test_util.c | 7 - tools/testing/selftests/kvm/lib/x86/sev.c | 2 +- .../testing/selftests/kvm/pre_fault_memory_test.c | 4 +- .../kvm/x86/guest_memfd_conversions_test.c | 552 +++++++++++++++++++ .../kvm/x86/private_mem_conversions_test.c | 55 +- .../kvm/x86/private_mem_conversions_test.sh | 128 +++++ .../selftests/kvm/x86/private_mem_kvm_exits_test.c | 38 +- virt/kvm/Kconfig | 3 +- virt/kvm/guest_memfd.c | 591 ++++++++++++++++++++- virt/kvm/kvm_main.c | 87 ++- 28 files changed, 2075 insertions(+), 190 deletions(-) --- base-commit: 39f1c201b93f4ff71631bac72cff6eb155f976a4 change-id: 20260225-gmem-inplace-conversion-bd0dbd39753a Best regards, -- Ackerley Tng