On Fri, 08 Mar 2024 17:09:24 -0800, Sean Christopherson wrote:
> First, rip out KVM's support for virtualizing guest MTRRs on VMX. The
> code is costly to main, a drag on guest boot performance, imperfect, and
> not required for functional correctness with modern guest kernels. Many
> details in patch 1's changelog.
>
> With MTRR virtualization gone, always honor guest PAT on Intel CPUs that
> support self-snoop, as such CPUs are guaranteed to maintain coherency
> even if the guest is aliasing memtypes, e.g. if the host is using WB but
> the guest is using WC. Honoring guest PAT is desirable for use cases
> where the guest must use WC when accessing memory that is DMA'd from a
> non-coherent device that does NOT bounce through VFIO, e.g. for mediated
> virtual GPUs.
>
> [...]
Applied to kvm-x86 mtrrs, to get as much testing as possible before a potential
merge in 6.11.
Paul, if you can take a gander at patch 3, it would be much appreciated.
Thanks!
[1/5] KVM: x86: Remove VMX support for virtualizing guest MTRR memtypes
https://github.com/kvm-x86/linux/commit/0a7b73559b39
[2/5] KVM: VMX: Drop support for forcing UC memory when guest CR0.CD=1
https://github.com/kvm-x86/linux/commit/e1548088ff54
[3/5] srcu: Add an API for a memory barrier after SRCU read lock
https://github.com/kvm-x86/linux/commit/fcfe671e0879
[4/5] KVM: x86: Ensure a full memory barrier is emitted in the VM-Exit path
https://github.com/kvm-x86/linux/commit/eb8d8fc29286
[5/5] KVM: VMX: Always honor guest PAT on CPUs that support self-snoop
https://github.com/kvm-x86/linux/commit/95200f24b862
--
https://github.com/kvm-x86/linux/tree/next
