[PATCH RFC v8 12/56] x86/sev: Add RMP entry lookup helpers

[Michael Roth <michael.roth@amd.com>]

From: Brijesh Singh <brijesh.singh@amd.com>

The snp_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 AMD PPR, see
https://bugzilla.kernel.org/attachment.cgi?id=296015.

Co-developed-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 arch/x86/include/asm/sev.h |  4 +-
 arch/x86/kernel/sev.c      | 84 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index ebc271bb6d8e..8d3ce2ad27da 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -83,7 +83,7 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
 
 /* RMP page size */
 #define RMP_PG_SIZE_4K			0
-
+#define RMP_TO_X86_PG_LEVEL(level)	(((level) == RMP_PG_SIZE_4K) ? PG_LEVEL_4K : PG_LEVEL_2M)
 #define RMPADJUST_VMSA_PAGE_BIT		BIT(16)
 
 /* SNP Guest message request */
@@ -197,6 +197,7 @@ void snp_set_wakeup_secondary_cpu(void);
 bool snp_init(struct boot_params *bp);
 void __init __noreturn snp_abort(void);
 int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned long *fw_err);
+int snp_lookup_rmpentry(u64 pfn, int *level);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
@@ -221,6 +222,7 @@ static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *in
 {
 	return -ENOTTY;
 }
+static inline int snp_lookup_rmpentry(u64 pfn, int *level) { return 0; }
 #endif
 
 #endif
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index e54e412c9916..a063c1b98034 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -61,11 +61,36 @@
 #define AP_INIT_CR0_DEFAULT		0x60000010
 #define AP_INIT_MXCSR_DEFAULT		0x1f80
 
+/*
+ * The RMP entry format is not architectural. The format is defined in PPR
+ * Family 19h Model 01h, Rev B1 processor.
+ */
+struct rmpentry {
+	union {
+		struct {
+			u64	assigned	: 1,
+				pagesize	: 1,
+				immutable	: 1,
+				rsvd1		: 9,
+				gpa		: 39,
+				asid		: 10,
+				vmsa		: 1,
+				validated	: 1,
+				rsvd2		: 1;
+		} info;
+		u64 low;
+	};
+	u64 high;
+} __packed;
+
 /*
  * The first 16KB from the RMP_BASE is used by the processor for the
  * bookkeeping, the range needs to be added during the RMP entry lookup.
  */
 #define RMPTABLE_CPU_BOOKKEEPING_SZ	0x4000
+#define RMPENTRY_SHIFT			8
+#define rmptable_page_offset(x)	(RMPTABLE_CPU_BOOKKEEPING_SZ + \
+				 (((unsigned long)x) >> RMPENTRY_SHIFT))
 
 /* For early boot hypervisor communication in SEV-ES enabled guests */
 static struct ghcb boot_ghcb_page __bss_decrypted __aligned(PAGE_SIZE);
@@ -2435,3 +2460,62 @@ static int __init snp_host_init(void)
  * the page(s) used for DMA are hypervisor owned.
  */
 fs_initcall(snp_host_init);
+
+static inline unsigned int rmpentry_assigned(struct rmpentry *e)
+{
+	return e->info.assigned;
+}
+
+static inline unsigned int rmpentry_pagesize(struct rmpentry *e)
+{
+	return e->info.pagesize;
+}
+
+static struct rmpentry *rmptable_entry(unsigned long paddr)
+{
+	unsigned long vaddr;
+
+	vaddr = rmptable_start + rmptable_page_offset(paddr);
+	if (unlikely(vaddr > rmptable_end))
+		return ERR_PTR(-EFAULT);
+
+	return (struct rmpentry *)vaddr;
+}
+
+static struct rmpentry *__snp_lookup_rmpentry(u64 pfn, int *level)
+{
+	unsigned long paddr = pfn << PAGE_SHIFT;
+	struct rmpentry *entry, *large_entry;
+
+	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
+		return ERR_PTR(-ENXIO);
+
+	if (!pfn_valid(pfn))
+		return ERR_PTR(-EINVAL);
+
+	entry = rmptable_entry(paddr);
+	if (IS_ERR(entry))
+		return entry;
+
+	/* Read a large RMP entry to get the correct page level used in RMP entry. */
+	large_entry = rmptable_entry(paddr & PMD_MASK);
+	*level = RMP_TO_X86_PG_LEVEL(rmpentry_pagesize(large_entry));
+
+	return entry;
+}
+
+/*
+ * Return 1 if the RMP entry is assigned, 0 if it exists but is not assigned,
+ * and -errno if there is no corresponding RMP entry.
+ */
+int snp_lookup_rmpentry(u64 pfn, int *level)
+{
+	struct rmpentry *e;
+
+	e = __snp_lookup_rmpentry(pfn, level);
+	if (IS_ERR(e))
+		return PTR_ERR(e);
+
+	return !!rmpentry_assigned(e);
+}
+EXPORT_SYMBOL_GPL(snp_lookup_rmpentry);
-- 
2.25.1