On Fri, 2025-05-02 at 16:08 +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) {
> + int nr = tdx_nr_pamt_pages(tdx_get_sysinfo());
> + r = kvm_mmu_topup_memory_cache(&vcpu->arch.pamt_page_cache,
> + nr * PT64_ROOT_MAX_LEVEL);
> + if (r)
> + return r;
> + }
> +
> return kvm_mmu_topup_memory_cache(&vcpu->arch.mmu_page_header_cache,
> PT64_ROOT_MAX_LEVEL);
> }
> @@ -626,6 +635,7 @@ static void mmu_free_memory_caches(struct kvm_vcpu *vcpu)
> kvm_mmu_free_memory_cache(&vcpu->arch.mmu_shadow_page_cache);
> kvm_mmu_free_memory_cache(&vcpu->arch.mmu_shadowed_info_cache);
> kvm_mmu_free_memory_cache(&vcpu->arch.mmu_external_spt_cache);
> + kvm_mmu_free_memory_cache(&vcpu->arch.pamt_page_cache);
> kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_header_cache);
> }
>
IIUC, this patch can be avoided if we create an actual kmem_cache for
mmu_external_spt_cache with an actual 'ctor' where we simply call
tdx_alloc_page() as replied to the previous patch.
