Re: [PATCH v2 0/7] KVM: x86/mmu: Zap only obsolete roots on "reload"

[Paolo Bonzini <pbonzini@redhat.com>]

On 2/25/22 19:22, Sean Christopherson wrote:
> For all intents and purposes, this is an x86/mmu series, but it touches
> s390 and common KVM code because KVM_REQ_MMU_RELOAD is currently a generic
> request despite its use being encapsulated entirely within arch code.
> 
> The meat of the series is to zap only obsolete (a.k.a. invalid) roots in
> response to KVM marking a root obsolete/invalid due to it being zapped.
> KVM currently drops/zaps all roots, which, aside from being a performance
> hit if the guest is using multiple roots, complicates x86 KVM paths that
> load a new root because it raises the question of what should be done if
> there's a pending KVM_REQ_MMU_RELOAD, i.e. if the path _knows_ that any
> root it loads will be obliterated.
> 
> Paolo, I'm hoping you can squash patch 01 with your patch it "fixes".
> 
> I'm also speculating that this will be applied after my patch to remove
> KVM_REQ_GPC_INVALIDATE, otherwise the changelog in patch 06 will be
> wrong.

Queued, thanks.

Paolo

> v2:
>   - Collect reviews. [Claudio, Janosch]
>   - Rebase to latest kvm/queue.
> 
> v1: https://lore.kernel.org/all/20211209060552.2956723-1-seanjc@google.com
> 
> Sean Christopherson (7):
>    KVM: x86: Remove spurious whitespaces from kvm_post_set_cr4()
>    KVM: x86: Invoke kvm_mmu_unload() directly on CR4.PCIDE change
>    KVM: Drop kvm_reload_remote_mmus(), open code request in x86 users
>    KVM: x86/mmu: Zap only obsolete roots if a root shadow page is zapped
>    KVM: s390: Replace KVM_REQ_MMU_RELOAD usage with arch specific request
>    KVM: Drop KVM_REQ_MMU_RELOAD and update vcpu-requests.rst
>      documentation
>    KVM: WARN if is_unsync_root() is called on a root without a shadow
>      page
> 
>   Documentation/virt/kvm/vcpu-requests.rst |  7 +-
>   arch/s390/include/asm/kvm_host.h         |  2 +
>   arch/s390/kvm/kvm-s390.c                 |  8 +--
>   arch/s390/kvm/kvm-s390.h                 |  2 +-
>   arch/x86/include/asm/kvm_host.h          |  2 +
>   arch/x86/kvm/mmu.h                       |  1 +
>   arch/x86/kvm/mmu/mmu.c                   | 83 ++++++++++++++++++++----
>   arch/x86/kvm/x86.c                       | 10 +--
>   include/linux/kvm_host.h                 |  4 +-
>   virt/kvm/kvm_main.c                      |  5 --
>   10 files changed, 90 insertions(+), 34 deletions(-)
> 
> 
> base-commit: f4bc051fc91ab9f1d5225d94e52d369ef58bec58