[PATCH Part2 RFC v2 06/37] x86/sev: Add RMP entry lookup helpers

[Brijesh Singh]

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.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/include/asm/sev.h |  5 +---
 arch/x86/kernel/sev.c      | 28 ++++++++++++++++++++
 include/linux/sev.h        | 54 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 83 insertions(+), 4 deletions(-)
 create mode 100644 include/linux/sev.h

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 7f4c34dd84e1..a65e78fa3d51 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -9,6 +9,7 @@
 #define __ASM_ENCRYPTED_STATE_H
 
 #include <linux/types.h>
+#include <linux/sev.h>
 #include <asm/insn.h>
 #include <asm/sev-common.h>
 
@@ -65,10 +66,6 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
 #define PVALIDATE_FAIL_SIZEMISMATCH	6
 #define PVALIDATE_FAIL_NOUPDATE		255 /* Software defined (when rFlags.CF = 1) */
 
-/* RMP page size */
-#define RMP_PG_SIZE_2M			1
-#define RMP_PG_SIZE_4K			0
-
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 extern struct static_key_false sev_es_enable_key;
 extern void __sev_es_ist_enter(struct pt_regs *regs);
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 126fa441c0f8..dec4f423e232 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -40,6 +40,10 @@
 
 #define DR7_RESET_VALUE        0x400
 
+#define RMPTABLE_ENTRIES_OFFSET	0x4000
+#define RMPENTRY_SHIFT		8
+#define rmptable_page_offset(x)	(RMPTABLE_ENTRIES_OFFSET + (((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);
 
@@ -1873,3 +1877,27 @@ static int __init snp_rmptable_init(void)
 	return 0;
 }
 early_initcall(snp_rmptable_init);
+
+struct rmpentry *snp_lookup_page_in_rmptable(struct page *page, int *level)
+{
+	unsigned long phys = page_to_pfn(page) << PAGE_SHIFT;
+	struct rmpentry *entry, *large_entry;
+	unsigned long vaddr;
+
+	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
+		return NULL;
+
+	vaddr = rmptable_start + rmptable_page_offset(phys);
+	if (unlikely(vaddr > rmptable_end))
+		return NULL;
+
+	entry = (struct rmpentry *)vaddr;
+
+	/* Read a large RMP entry to get the correct page level used in RMP entry. */
+	vaddr = rmptable_start + rmptable_page_offset(phys & PMD_MASK);
+	large_entry = (struct rmpentry *)vaddr;
+	*level = RMP_TO_X86_PG_LEVEL(rmpentry_pagesize(large_entry));
+
+	return entry;
+}
+EXPORT_SYMBOL_GPL(snp_lookup_page_in_rmptable);
diff --git a/include/linux/sev.h b/include/linux/sev.h
new file mode 100644
index 000000000000..ee038d466786
--- /dev/null
+++ b/include/linux/sev.h
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * AMD Secure Encrypted Virtualization
+ *
+ * Author: Brijesh Singh <brijesh.singh@xxxxxxx>
+ */
+
+#ifndef __LINUX_SEV_H
+#define __LINUX_SEV_H
+
+struct __packed rmpentry {
+	union {
+		struct {
+			u64 assigned:1;
+			u64 pagesize:1;
+			u64 immutable:1;
+			u64 rsvd1:9;
+			u64 gpa:39;
+			u64 asid:10;
+			u64 vmsa:1;
+			u64 validated:1;
+			u64 rsvd2:1;
+		} info;
+		u64 low;
+	};
+	u64 high;
+};
+
+#define rmpentry_assigned(x)	((x)->info.assigned)
+#define rmpentry_pagesize(x)	((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)
+
+/* RMP page size */
+#define RMP_PG_SIZE_2M			1
+#define RMP_PG_SIZE_4K			0
+
+/* Macro to convert the x86 page level to the RMP level and vice versa */
+#define X86_TO_RMP_PG_LEVEL(level)	(((level) == PG_LEVEL_4K) ? RMP_PG_SIZE_4K : RMP_PG_SIZE_2M)
+#define RMP_TO_X86_PG_LEVEL(level)	(((level) == RMP_PG_SIZE_4K) ? PG_LEVEL_4K : PG_LEVEL_2M)
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+struct rmpentry *snp_lookup_page_in_rmptable(struct page *page, int *level);
+#else
+static inline struct rmpentry *snp_lookup_page_in_rmptable(struct page *page, int *level)
+{
+	return NULL;
+}
+
+#endif /* CONFIG_AMD_MEM_ENCRYPT */
+#endif /* __LINUX_SEV_H */
-- 
2.17.1