> 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. > > The SRCU patch adds an API that is effectively documentation for the > memory barrier in srcu_read_lock(). Intel CPUs with self-snoop require a > memory barrier after VM-Exit to ensure coherency, and KVM always does a > srcu_read_lock() before reading guest memory after VM-Exit. Relying on > SRCU to provide the barrier allows KVM to avoid emitting a redundant barrier > of its own. > > This series needs a _lot_ more testing; I arguably should have tagged it RFC, > but I'm feeling lucky. > > Sean Christopherson (3): > KVM: x86: Remove VMX support for virtualizing guest MTRR memtypes > KVM: VMX: Drop support for forcing UC memory when guest CR0.CD=1 > KVM: VMX: Always honor guest PAT on CPUs that support self-snoop > > Yan Zhao (2): > srcu: Add an API for a memory barrier after SRCU read lock > KVM: x86: Ensure a full memory barrier is emitted in the VM-Exit path > > Documentation/virt/kvm/api.rst | 6 +- > Documentation/virt/kvm/x86/errata.rst | 18 + > arch/x86/include/asm/kvm_host.h | 15 +- > arch/x86/kvm/mmu.h | 7 +- > arch/x86/kvm/mmu/mmu.c | 35 +- > arch/x86/kvm/mtrr.c | 644 ++------------------------ > arch/x86/kvm/vmx/vmx.c | 40 +- > arch/x86/kvm/x86.c | 24 +- > arch/x86/kvm/x86.h | 4 - > include/linux/srcu.h | 14 + > 10 files changed, 105 insertions(+), 702 deletions(-) > > > base-commit: 964d0c614c7f71917305a5afdca9178fe8231434 > -- > 2.44.0.278.ge034bb2e1d-goog > Verified iGPU passthrough(GVT-d) on Intel platforms, TGL Core(TM) i5-1135G7/ADL Core(TM) i7-12700/RPL/MTL Ultra 7 + Ubuntu22.04 LTS. Both Linux Ubuntu 22.04 VM and Windows10 VM could boot up successfully. 3D benchmark GLmark2 can run as expected in the guest VM. Tested-by: Yongwei Ma <yongwei.ma@xxxxxxxxx> Best Regards, Yongwei Ma
