On Wed, May 14, 2025 at 02:30:34PM +0800, Chao Gao wrote:
> On Fri, May 02, 2025 at 04:08:25PM +0300, Kirill A. Shutemov wrote:
> >Preallocate a page to be used in the link_external_spt() and
> >set_external_spte() paths.
> >
> >In the worst-case scenario, handling a page fault might require a
> >tdx_nr_pamt_pages() pages for each page table level.
> >
> >Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> >---
> > arch/x86/include/asm/kvm_host.h | 2 ++
> > arch/x86/kvm/mmu/mmu.c | 10 ++++++++++
> > 2 files changed, 12 insertions(+)
> >
> >diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> >index 91958c55f918..a5661499a176 100644
> >--- a/arch/x86/include/asm/kvm_host.h
> >+++ b/arch/x86/include/asm/kvm_host.h
> >@@ -849,6 +849,8 @@ struct kvm_vcpu_arch {
> > */
> > struct kvm_mmu_memory_cache mmu_external_spt_cache;
> >
> >+ struct kvm_mmu_memory_cache pamt_page_cache;
> >+
> > /*
> > * QEMU userspace and the guest each have their own FPU state.
> > * In vcpu_run, we switch between the user and guest FPU contexts.
> >diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> >index a284dce227a0..7bfa0dc50440 100644
> >--- a/arch/x86/kvm/mmu/mmu.c
> >+++ b/arch/x86/kvm/mmu/mmu.c
> >@@ -616,6 +616,15 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
> > if (r)
> > return r;
> > }
> >+
> >+ if (vcpu->kvm->arch.vm_type == KVM_X86_TDX_VM) {
>
> The check for vcpu->kvm->arch.vm_type == KVM_X86_TDX_VM is identical to
> kvm_has_mirrored_tdp() a few lines above.
Well, yes. But I think it is conceptually different. There can be
different virtualization mode that has mirrored TDP which is not TDX.
>
> >+ int nr = tdx_nr_pamt_pages(tdx_get_sysinfo());
>
> Since you're already accessing tdx_sysinfo, you can check if dynamic PAMT is
> enabled and allocate the pamt page cache accordingly.
I will hide it in tdx_nr_pamt_pages() which would return 0 if Dynamic PAMT
is disabled.
--
Kiryl Shutsemau / Kirill A. Shutemov
