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| author | Sean Christopherson <seanjc@google.com> | 2024-03-09 04:09:26 +0300 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2024-06-05 18:13:14 +0300 |
| commit | e1548088ff544e4a4ae2c960bccf0eeff3a46297 (patch) | |
| tree | 44eed91ec9a6107f900f487e95288456fcd86e0b /arch/x86/kvm/vmx | |
| parent | 0a7b73559b39497fae1b7b3d4bab69895097c37e (diff) | |
| download | linux-e1548088ff544e4a4ae2c960bccf0eeff3a46297.tar.xz | |
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 'arch/x86/kvm/vmx')
| -rw-r--r-- | arch/x86/kvm/vmx/vmx.c | 4 |
1 files changed, 0 insertions, 4 deletions
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index dec3de308ea8..a3cc0bc30540 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -7674,10 +7674,6 @@ u8 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio) if (!kvm_arch_has_noncoherent_dma(vcpu->kvm)) return (MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT) | VMX_EPT_IPAT_BIT; - if (kvm_read_cr0_bits(vcpu, X86_CR0_CD) && - !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED)) - return (MTRR_TYPE_UNCACHABLE << VMX_EPT_MT_EPTE_SHIFT) | VMX_EPT_IPAT_BIT; - return (MTRR_TYPE_WRBACK << VMX_EPT_MT_EPTE_SHIFT); } |