diff options
| author | Sean Christopherson <seanjc@google.com> | 2024-03-08 17:09:26 -0800 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2024-06-05 08:13:14 -0700 |
| commit | e1548088ff544e4a4ae2c960bccf0eeff3a46297 (patch) | |
| tree | 44eed91ec9a6107f900f487e95288456fcd86e0b /Documentation/virt/kvm/api.rst | |
| parent | 0a7b73559b39497fae1b7b3d4bab69895097c37e (diff) | |
KVM: VMX: Drop support for forcing UC memory when guest CR0.CD=1
Drop KVM's emulation of CR0.CD=1 on Intel CPUs now that KVM no longer
honors guest MTRR memtypes, as forcing UC memory for VMs with
non-coherent DMA only makes sense if the guest is using something other
than PAT to configure the memtype for the DMA region.
Furthermore, KVM has forced WB memory for CR0.CD=1 since commit
fb279950ba02 ("KVM: vmx: obey KVM_QUIRK_CD_NW_CLEARED"), and no known
VMM in existence disables KVM_X86_QUIRK_CD_NW_CLEARED, let alone does
so with non-coherent DMA.
Lastly, commit fb279950ba02 ("KVM: vmx: obey KVM_QUIRK_CD_NW_CLEARED") was
from the same author as commit b18d5431acc7 ("KVM: x86: fix CR0.CD
virtualization"), and followed by a mere month. I.e. forcing UC memory
was likely the result of code inspection or perhaps misdiagnosed failures,
and not the necessitate by a concrete use case.
Update KVM's documentation to note that KVM_X86_QUIRK_CD_NW_CLEARED is now
AMD-only, and to take an erratum for lack of CR0.CD virtualization on
Intel.
Tested-by: Xiangfei Ma <xiangfeix.ma@intel.com>
Tested-by: Yongwei Ma <yongwei.ma@intel.com>
Link: https://lore.kernel.org/r/20240309010929.1403984-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'Documentation/virt/kvm/api.rst')
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index a71d91978d9e..298167363706 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -7953,7 +7953,11 @@ The valid bits in cap.args[0] are: When this quirk is disabled, the reset value is 0x10000 (APIC_LVT_MASKED). - KVM_X86_QUIRK_CD_NW_CLEARED By default, KVM clears CR0.CD and CR0.NW. + KVM_X86_QUIRK_CD_NW_CLEARED By default, KVM clears CR0.CD and CR0.NW on + AMD CPUs to workaround buggy guest firmware + that runs in perpetuity with CR0.CD, i.e. + with caches in "no fill" mode. + When this quirk is disabled, KVM does not change the value of CR0.CD and CR0.NW. |