linux-kernel - [RFC, PATCH 09/12] KVM: TDX: Preallocate PAMT pages to be used in page fault path

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Message-ID: <20250502130828.4071412-10-kirill.shutemov@linux.intel.com>
Date: Fri,  2 May 2025 16:08:25 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com
Cc: rick.p.edgecombe@...el.com,
	isaku.yamahata@...el.com,
	kai.huang@...el.com,
	yan.y.zhao@...el.com,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	kvm@...r.kernel.org,
	x86@...nel.org,
	linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [RFC, PATCH 09/12] KVM: TDX: Preallocate PAMT pages to be used in page fault path

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@...ux.intel.com>
---
 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);
 }
 
-- 
2.47.2