[PATCH Part2 RFC v4 05/40] 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 |  4 +--
 arch/x86/kernel/sev.c      | 26 +++++++++++++++++++
 include/linux/sev.h        | 51 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 78 insertions(+), 3 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 6c23e694a109..9e7e7e737f55 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>
 #include <asm/bootparam.h>
@@ -75,9 +76,6 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
 /* Software defined (when rFlags.CF = 1) */
 #define PVALIDATE_FAIL_NOUPDATE		255
 
-/* RMP page size */
-#define RMP_PG_SIZE_4K			0
-
 #define RMPADJUST_VMSA_PAGE_BIT		BIT(16)
 
 #ifdef CONFIG_AMD_MEM_ENCRYPT
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index f9d813d498fa..1aed3d53f59f 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -49,6 +49,8 @@
 #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);
@@ -2319,3 +2321,27 @@ static int __init snp_rmptable_init(void)
  * passthough state, and it is available after subsys_initcall().
  */
 fs_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..83c89e999999
--- /dev/null
+++ b/include/linux/sev.h
@@ -0,0 +1,51 @@
+/* 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,
+				pagesize	: 1,
+				immutable	: 1,
+				rsvd1		: 9,
+				gpa		: 39,
+				asid		: 10,
+				vmsa		: 1,
+				validated	: 1,
+				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_4K			0
+
+#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