[RFC Part2 PATCH 02/30] x86/sev-snp: add RMP entry lookup helpers

[Brijesh Singh]

The lookup_page_in_rmptable() can be used by the host to read the RMP
entry for a given page. The RMP entry format is documented in PPR
section 2.1.5.2.

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Joerg Roedel <jroedel@xxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/include/asm/sev-snp.h | 31 +++++++++++++++++++++++++++++++
 arch/x86/mm/mem_encrypt.c      | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 63 insertions(+)

diff --git a/arch/x86/include/asm/sev-snp.h b/arch/x86/include/asm/sev-snp.h
index f7280d5c6158..2aa14b38c5ed 100644
--- a/arch/x86/include/asm/sev-snp.h
+++ b/arch/x86/include/asm/sev-snp.h
@@ -67,6 +67,35 @@ struct __packed snp_page_state_change {
 #define X86_RMP_PG_LEVEL(level)	(((level) == PG_LEVEL_4K) ? RMP_PG_SIZE_4K : RMP_PG_SIZE_2M)
 #define RMP_X86_PG_LEVEL(level)	(((level) == RMP_PG_SIZE_4K) ? PG_LEVEL_4K : PG_LEVEL_2M)
 
+/* RMP table entry format (PPR section 2.1.5.2) */
+struct __packed rmpentry {
+	union {
+		struct {
+			uint64_t assigned:1;
+			uint64_t pagesize:1;
+			uint64_t immutable:1;
+			uint64_t rsvd1:9;
+			uint64_t gpa:39;
+			uint64_t asid:10;
+			uint64_t vmsa:1;
+			uint64_t validated:1;
+			uint64_t rsvd2:1;
+		} info;
+		uint64_t low;
+	};
+	uint64_t high;
+};
+
+typedef struct rmpentry rmpentry_t;
+
+#define rmpentry_assigned(x)	((x)->info.assigned)
+#define rmpentry_pagesize(x)	(RMP_X86_PG_LEVEL((x)->info.pagesize))
+#define rmpentry_vmsa(x)	((x)->info.vmsa)
+#define rmpentry_asid(x)	((x)->info.asid)
+#define rmpentry_validated(x)	((x)->info.validated)
+#define rmpentry_gpa(x)		((unsigned long)(x)->info.gpa)
+#define rmpentry_immutable(x)	((x)->info.immutable)
+
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 #include <linux/jump_label.h>
 
@@ -94,6 +123,7 @@ void __init early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr
 		unsigned int npages);
 int snp_set_memory_shared(unsigned long vaddr, unsigned int npages);
 int snp_set_memory_private(unsigned long vaddr, unsigned int npages);
+rmpentry_t *lookup_page_in_rmptable(struct page *page, int *level);
 
 extern struct static_key_false snp_enable_key;
 static inline bool snp_key_active(void)
@@ -124,6 +154,7 @@ early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr, unsigned i
 static inline int snp_set_memory_shared(unsigned long vaddr, unsigned int npages) { return 0; }
 static inline int snp_set_memory_private(unsigned long vaddr, unsigned int npages) { return 0; }
 static inline bool snp_key_active(void) { return false; }
+static inline rpmentry_t *lookup_page_in_rmptable(struct page *page, int *level) { return NULL; }
 
 #endif /* CONFIG_AMD_MEM_ENCRYPT */
 
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index 39461b9cb34e..06394b6d56b2 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -34,6 +34,8 @@
 
 #include "mm_internal.h"
 
+#define rmptable_page_offset(x)	(0x4000 + (((unsigned long) x) >> 8))
+
 /*
  * Since SME related variables are set early in the boot process they must
  * reside in the .data section so as not to be zeroed out when the .bss
@@ -612,3 +614,33 @@ static int __init mem_encrypt_snp_init(void)
  * SEV-SNP must be enabled across all CPUs, so make the initialization as a late initcall.
  */
 late_initcall(mem_encrypt_snp_init);
+
+rmpentry_t *lookup_page_in_rmptable(struct page *page, int *level)
+{
+	unsigned long phys = page_to_pfn(page) << PAGE_SHIFT;
+	rmpentry_t *entry, *large_entry;
+	unsigned long vaddr;
+
+	if (!static_branch_unlikely(&snp_enable_key))
+		return NULL;
+
+	vaddr = rmptable_start + rmptable_page_offset(phys);
+	if (WARN_ON(vaddr > rmptable_end))
+		return NULL;
+
+	entry = (rmpentry_t *)vaddr;
+
+	/*
+	 * Check if this page is covered by the large RMP entry. This is needed to get
+	 * the page level used in the RMP entry.
+	 *
+	 * e.g. if the page is covered by the large RMP entry then page size is set in the
+	 *       base RMP entry.
+	 */
+	vaddr = rmptable_start + rmptable_page_offset(phys & PMD_MASK);
+	large_entry = (rmpentry_t *)vaddr;
+	*level = rmpentry_pagesize(large_entry);
+
+	return entry;
+}
+EXPORT_SYMBOL_GPL(lookup_page_in_rmptable);
-- 
2.17.1