linux-kernel - [PATCHv2 07/12] KVM: TDX: Preallocate PAMT pages to be used in page fault path

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Message-ID: <20250609191340.2051741-8-kirill.shutemov@linux.intel.com>
Date: Mon,  9 Jun 2025 22:13:35 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com,
	dave.hansen@...ux.intel.com
Cc: rick.p.edgecombe@...el.com,
	isaku.yamahata@...el.com,
	kai.huang@...el.com,
	yan.y.zhao@...el.com,
	chao.gao@...el.com,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	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: [PATCHv2 07/12] 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/include/asm/tdx.h      | 2 ++
 arch/x86/kvm/mmu/mmu.c          | 7 +++++++
 arch/x86/virt/vmx/tdx/tdx.c     | 3 ++-
 4 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 330cdcbed1a6..02dbbf848182 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/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index d9a77147412f..47092eb13eb3 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -115,6 +115,7 @@ int tdx_guest_keyid_alloc(void);
 u32 tdx_get_nr_guest_keyids(void);
 void tdx_guest_keyid_free(unsigned int keyid);
 
+int tdx_nr_pamt_pages(void);
 struct page *tdx_alloc_page(void);
 void tdx_free_page(struct page *page);
 
@@ -188,6 +189,7 @@ static inline int tdx_enable(void)  { return -ENODEV; }
 static inline u32 tdx_get_nr_guest_keyids(void) { return 0; }
 static inline const char *tdx_dump_mce_info(struct mce *m) { return NULL; }
 static inline const struct tdx_sys_info *tdx_get_sysinfo(void) { return NULL; }
+static inline int tdx_nr_pamt_pages(void) { return 0; }
 #endif	/* CONFIG_INTEL_TDX_HOST */
 
 #endif /* !__ASSEMBLER__ */
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index cbc84c6abc2e..d99bb27b5b01 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -616,6 +616,12 @@ static int mmu_topup_memory_caches(struct kvm_vcpu *vcpu, bool maybe_indirect)
 		if (r)
 			return r;
 	}
+
+	r = kvm_mmu_topup_memory_cache(&vcpu->arch.pamt_page_cache,
+				       tdx_nr_pamt_pages() * 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 +632,7 @@ 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);
 }
 
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index c514c60e8c8d..4f9eaba4af4a 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -2001,13 +2001,14 @@ u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page)
 }
 EXPORT_SYMBOL_GPL(tdh_phymem_page_wbinvd_hkid);
 
-static int tdx_nr_pamt_pages(void)
+int tdx_nr_pamt_pages(void)
 {
 	if (!tdx_supports_dynamic_pamt(&tdx_sysinfo))
 		return 0;
 
 	return tdx_sysinfo.tdmr.pamt_4k_entry_size * PTRS_PER_PTE / PAGE_SIZE;
 }
+EXPORT_SYMBOL_GPL(tdx_nr_pamt_pages);
 
 static u64 tdh_phymem_pamt_add(unsigned long hpa,
 			       struct list_head *pamt_pages)
-- 
2.47.2