[v18,035/121] KVM: Allow page-sized MMU caches to be initialized with custom 64-bit values

Commit Message

Isaku Yamahata Jan. 22, 2024, 11:53 p.m. UTC

From: Sean Christopherson <[e-mail]>

Add support to MMU caches for initializing a page with a custom 64-bit
value, e.g. to pre-fill an entire page table with non-zero PTE values.
The functionality will be used by x86 to support Intel's TDX, which needs
to set bit 63 in all non-present PTEs in order to prevent !PRESENT page
faults from getting reflected into the guest (Intel's EPT Violation #VE
architecture made the less than brilliant decision of having the per-PTE
behavior be opt-out instead of opt-in).

Signed-off-by: Sean Christopherson <[e-mail]>
Signed-off-by: Isaku Yamahata <[e-mail]>
---
 include/linux/kvm_types.h |  1 +
 virt/kvm/kvm_main.c       | 16 ++++++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

Patch

diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
index 9d1f7835d8c1..60c8d5c9eab9 100644
--- a/include/linux/kvm_types.h
+++ b/include/linux/kvm_types.h
@@ -94,6 +94,7 @@  struct gfn_to_pfn_cache {
 struct kvm_mmu_memory_cache {
 	gfp_t gfp_zero;
 	gfp_t gfp_custom;
+	u64 init_value;
 	struct kmem_cache *kmem_cache;
 	int capacity;
 	int nobjs;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 48f2086a627f..0a0f3b131ea2 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -401,12 +401,17 @@  static void kvm_flush_shadow_all(struct kvm *kvm)
 static inline void *mmu_memory_cache_alloc_obj(struct kvm_mmu_memory_cache *mc,
 					       gfp_t gfp_flags)
 {
+	void *page;
+
 	gfp_flags |= mc->gfp_zero;
 
 	if (mc->kmem_cache)
 		return kmem_cache_alloc(mc->kmem_cache, gfp_flags);
-	else
-		return (void *)__get_free_page(gfp_flags);
+
+	page = (void *)__get_free_page(gfp_flags);
+	if (page && mc->init_value)
+		memset64(page, mc->init_value, PAGE_SIZE / sizeof(mc->init_value));
+	return page;
 }
 
 int __kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int capacity, int min)
@@ -421,6 +426,13 @@  int __kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int capacity,
 		if (WARN_ON_ONCE(!capacity))
 			return -EIO;
 
+		/*
+		 * Custom init values can be used only for page allocations,
+		 * and obviously conflict with __GFP_ZERO.
+		 */
+		if (WARN_ON_ONCE(mc->init_value && (mc->kmem_cache || mc->gfp_zero)))
+			return -EIO;
+
 		mc->objects = kvmalloc_array(sizeof(void *), capacity, gfp);
 		if (!mc->objects)
 			return -ENOMEM;