From: Sean Christopherson <seanjc@google.com>
To: Fuad Tabba <tabba@google.com>
Cc: ackerleytng@google.com, aik@amd.com, andrew.jones@linux.dev,
binbin.wu@linux.intel.com, brauner@kernel.org,
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linux-coco@lists.linux.dev
Subject: Re: [PATCH v6 19/43] KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes
Date: Thu, 21 May 2026 07:21:42 -0700 [thread overview]
Message-ID: <ag8U9qIcTd_GykHE@google.com> (raw)
In-Reply-To: <CA+EHjTzu=28Sr3=9A9LmJEGz0tBEDbU9taznVV5kdL7s8Nw=Jg@mail.gmail.com>
On Thu, May 21, 2026, Fuad Tabba wrote:
> Hi Ackerley,
>
> On Thu, 7 May 2026 at 21:22, Ackerley Tng via B4 Relay
> <devnull+ackerleytng.google.com@kernel.org> wrote:
> >
> > From: Sean Christopherson <seanjc@google.com>
> >
> > Make vm_memory_attributes a module parameter so that userspace can disable
> > the use of memory attributes on the VM level.
> >
> > To avoid inconsistencies in the way memory attributes are tracked in KVM
> > and guest_memfd, the vm_memory_attributes module_param is made
> > read-only (0444).
> >
> > Make CONFIG_KVM_VM_MEMORY_ATTRIBUTES selectable, only for (CoCo) VM types
> > that might use vm_memory_attributes.
> >
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > Signed-off-by: Ackerley Tng <ackerleytng@google.com>
>
> Config files always confuse me, but Sashiko might be onto something:
>
> https://sashiko.dev/#/patchset/20260507-gmem-inplace-conversion-v6-0-91ab5a8b19a4%40google.com?part=19
: Since this prompt does not have a default value, will it default to N
: and silently drop KVM_VM_MEMORY_ATTRIBUTES during configuration updates
: like make olddefconfig?
:
: Existing userspace VMMs that rely on the KVM_SET_MEMORY_ATTRIBUTES ioctl
: for TDX or SEV VMs might fail to boot if the feature is unexpectedly
: compiled out. Could a default y be used to preserve backwards
: compatibility for existing configurations?
> I think this partially goes back to commit 6, the one I flagged
> yesterday. But also adding "default y" to KVM_VM_MEMORY_ATTRIBUTES?
> The default value should at least fix this issue, but I'm not sure if
> it would cause other problems...
Hrm. As much as I want per-gmem attributes to be the default going forward,
silently breaking existing setups isn't great. On the other hand, I'm *very*
skeptical there are any SNP or TDX deployments using a distro kernel, so I'm
still leaning towards forcing the issue and turning per-VM attributes off by
default.
next prev parent reply other threads:[~2026-05-21 14:21 UTC|newest]
Thread overview: 91+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-07 20:22 [PATCH v6 00/43] guest_memfd: In-place conversion support Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 01/43] KVM: guest_memfd: Introduce per-gmem attributes, use to guard user mappings Ackerley Tng via B4 Relay
2026-05-08 23:36 ` Ackerley Tng
2026-05-07 20:22 ` [PATCH v6 02/43] KVM: Rename KVM_GENERIC_MEMORY_ATTRIBUTES to KVM_VM_MEMORY_ATTRIBUTES Ackerley Tng via B4 Relay
2026-05-20 12:08 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 03/43] KVM: Enumerate support for PRIVATE memory iff kvm_arch_has_private_mem is defined Ackerley Tng via B4 Relay
2026-05-20 12:08 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 04/43] KVM: Stub in ability to disable per-VM memory attribute tracking Ackerley Tng via B4 Relay
2026-05-20 12:08 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 05/43] KVM: guest_memfd: Wire up kvm_get_memory_attributes() to per-gmem attributes Ackerley Tng via B4 Relay
2026-05-20 12:08 ` Fuad Tabba
2026-05-20 18:59 ` Sean Christopherson
2026-05-20 21:44 ` Ackerley Tng
2026-05-21 7:19 ` Fuad Tabba
2026-05-21 13:31 ` Sean Christopherson
2026-05-21 13:48 ` Fuad Tabba
2026-05-21 14:29 ` Ackerley Tng
2026-05-07 20:22 ` [PATCH v6 06/43] KVM: x86/mmu: Bug the VM if gmem attributes are queried to determine max mapping level Ackerley Tng via B4 Relay
2026-05-20 13:33 ` Fuad Tabba
2026-05-20 14:21 ` Sean Christopherson
2026-05-20 20:25 ` Ackerley Tng
2026-05-20 20:39 ` Sean Christopherson
2026-05-07 20:22 ` [PATCH v6 07/43] KVM: guest_memfd: Update kvm_gmem_populate() to use gmem attributes Ackerley Tng via B4 Relay
2026-05-20 13:47 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 08/43] KVM: guest_memfd: Only prepare folios for private pages Ackerley Tng via B4 Relay
2026-05-20 13:51 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 09/43] KVM: Move kvm_supported_mem_attributes() to kvm_host.h Ackerley Tng via B4 Relay
2026-05-20 13:53 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 10/43] KVM: guest_memfd: Add base support for KVM_SET_MEMORY_ATTRIBUTES2 Ackerley Tng via B4 Relay
2026-05-20 14:00 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 11/43] KVM: guest_memfd: Ensure pages are not in use before conversion Ackerley Tng via B4 Relay
2026-05-20 14:28 ` Fuad Tabba
2026-05-21 7:09 ` Fuad Tabba
2026-05-21 14:36 ` Ackerley Tng
2026-05-07 20:22 ` [PATCH v6 12/43] KVM: guest_memfd: Call arch invalidate hooks on conversion Ackerley Tng via B4 Relay
2026-05-20 14:30 ` Fuad Tabba
2026-05-20 20:35 ` Ackerley Tng
2026-05-07 20:22 ` [PATCH v6 13/43] KVM: guest_memfd: Return early if range already has requested attributes Ackerley Tng via B4 Relay
2026-05-20 14:44 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 14/43] KVM: guest_memfd: Advertise KVM_SET_MEMORY_ATTRIBUTES2 ioctl Ackerley Tng via B4 Relay
2026-05-20 15:22 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 15/43] KVM: guest_memfd: Handle lru_add fbatch refcounts during conversion safety check Ackerley Tng via B4 Relay
2026-05-21 7:13 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 16/43] KVM: guest_memfd: Use actual size for invalidation in kvm_gmem_release() Ackerley Tng via B4 Relay
2026-05-21 7:30 ` Fuad Tabba
2026-05-21 12:59 ` Sean Christopherson
2026-05-21 13:29 ` Fuad Tabba
2026-05-21 14:40 ` Ackerley Tng
2026-05-07 20:22 ` [PATCH v6 17/43] KVM: guest_memfd: Determine invalidation filter from memory attributes Ackerley Tng via B4 Relay
2026-05-21 7:56 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 18/43] KVM: Move KVM_VM_MEMORY_ATTRIBUTES config definition to x86 Ackerley Tng via B4 Relay
2026-05-21 8:07 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 19/43] KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes Ackerley Tng via B4 Relay
2026-05-21 8:44 ` Fuad Tabba
2026-05-21 14:21 ` Sean Christopherson [this message]
2026-05-07 20:22 ` [PATCH v6 20/43] KVM: guest_memfd: Enable INIT_SHARED on guest_memfd for x86 Coco VMs Ackerley Tng via B4 Relay
2026-05-20 22:04 ` Ackerley Tng
2026-05-21 8:54 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 21/43] KVM: SEV: Make 'uaddr' parameter optional for KVM_SEV_SNP_LAUNCH_UPDATE Ackerley Tng via B4 Relay
2026-05-21 9:55 ` Fuad Tabba
2026-05-21 13:21 ` Sean Christopherson
2026-05-07 20:22 ` [PATCH v6 22/43] KVM: TDX: Make source page optional for KVM_TDX_INIT_MEM_REGION Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 23/43] KVM: selftests: Create gmem fd before "regular" fd when adding memslot Ackerley Tng via B4 Relay
2026-05-21 12:11 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 24/43] KVM: selftests: Rename guest_memfd{,_offset} to gmem_{fd,offset} Ackerley Tng via B4 Relay
2026-05-21 12:13 ` Fuad Tabba
2026-05-07 20:22 ` [PATCH v6 25/43] KVM: selftests: Add support for mmap() on guest_memfd in core library Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 26/43] KVM: selftests: Add selftests global for guest memory attributes capability Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 27/43] KVM: selftests: Add helpers for calling ioctls on guest_memfd Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 28/43] KVM: selftests: Test basic single-page conversion flow Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 29/43] KVM: selftests: Test conversion flow when INIT_SHARED Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 30/43] KVM: selftests: Test conversion precision in guest_memfd Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 31/43] KVM: selftests: Test conversion before allocation Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 32/43] KVM: selftests: Convert with allocated folios in different layouts Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 33/43] KVM: selftests: Test that truncation does not change shared/private status Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 34/43] KVM: selftests: Test that shared/private status is consistent across processes Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 35/43] KVM: selftests: Test conversion with elevated page refcount Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 36/43] KVM: selftests: Reset shared memory after hole-punching Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 37/43] KVM: selftests: Provide function to look up guest_memfd details from gpa Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 38/43] KVM: selftests: Provide common function to set memory attributes Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 39/43] KVM: selftests: Check fd/flags provided to mmap() when setting up memslot Ackerley Tng via B4 Relay
2026-05-07 20:22 ` [PATCH v6 40/43] KVM: selftests: Make TEST_EXPECT_SIGBUS thread-safe Ackerley Tng via B4 Relay
2026-05-07 20:23 ` [PATCH v6 41/43] KVM: selftests: Update private_mem_conversions_test to mmap() guest_memfd Ackerley Tng via B4 Relay
2026-05-07 20:23 ` [PATCH v6 42/43] KVM: selftests: Add script to exercise private_mem_conversions_test Ackerley Tng via B4 Relay
2026-05-07 20:23 ` [PATCH v6 43/43] KVM: selftests: Update private memory exits test to work with per-gmem attributes Ackerley Tng via B4 Relay
2026-05-07 20:34 ` [POC PATCH 0/5] guest_memfd in-place conversion selftests for SNP Ackerley Tng
2026-05-07 20:34 ` [POC PATCH 1/5] KVM: selftests: Initialize guest_memfd with INIT_SHARED Ackerley Tng
2026-05-07 20:34 ` [POC PATCH 2/5] KVM: selftests: Use guest_memfd memory contents in-place for SNP launch update Ackerley Tng
2026-05-07 20:34 ` [POC PATCH 3/5] KVM: selftests: Make guest_code_xsave more friendly Ackerley Tng
2026-05-07 20:34 ` [POC PATCH 4/5] KVM: selftests: Allow specifying CoCo-privateness while mapping a page Ackerley Tng
2026-05-07 20:34 ` [POC PATCH 5/5] KVM: selftests: Test conversions for SNP Ackerley Tng
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