Re: [PATCH v2 20/29] KVM: x86: Add KVM_REQ_MMU_SYNC_ALL_ROOTS

[Lai Jiangshan]

On Thu, Oct 08, 2026 at 12:14:16AM +0800, Yosry Ahmed wrote:
> Add a new x86 request to sync all roots, current and previous. This will
> be used when syncing the shadow NPTs on nested VMRUN when an ASID flush
> (or new ASID) is requested by L1, as all physical translations in all
> roots should be sync'd (since shadow mappings are not tagged with an
> ASID).
> 
> Refactor syncing all roots (currently only done by
> kvm_vcpu_flush_tlb_guest()) to a helper, and use it to handle the
> request.
> 
> Clear KVM_REQ_MMU_SYNC when handling KVM_REQ_MMU_SYNC_ALL_ROOTS as the
> latter is a superset. Do not do so inside kvm_mmu_sync_all_roots(), to
> avoid any subtle behavioral changes from kvm_vcpu_flush_tlb_guest()
> clearing KVM_REQ_MMU_SYNC. It makes sense to always clear it when
> syncing the MMU, but there might be weird dependencies on the sync only
> happening before the actual vCPU run, and kvm_vcpu_flush_tlb_guest() is
> called in other code paths than handling KVM_REQ_TLB_FLUSH_GUEST before
> vCPU run.
> 
> No functional change intended.

Reviewed-by: Lai Jiangshan <jiangshanlai@xxxxxxxxx>

> 
> Signed-off-by: Yosry Ahmed <yosry@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/kvm_host.h |  1 +
>  arch/x86/kvm/mmu.h              |  7 +++++++
>  arch/x86/kvm/x86.c              | 11 ++++++++---
>  3 files changed, 16 insertions(+), 3 deletions(-)
>