[PATCH RFC v9 10/51] x86/fault: Add helper for dumping RMP entries

[Michael Roth]

From: Brijesh Singh <brijesh.singh@xxxxxxx>

This information will be useful for debugging things like page faults
due to RMP access violations and RMPUPDATE failures.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
[mdr: move helper to standalone patch]
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
 arch/x86/coco/sev/host.c        | 43 +++++++++++++++++++++++++++++++++
 arch/x86/include/asm/sev-host.h |  2 ++
 2 files changed, 45 insertions(+)

diff --git a/arch/x86/coco/sev/host.c b/arch/x86/coco/sev/host.c
index 0cc5a6d11b25..d766b3bc6647 100644
--- a/arch/x86/coco/sev/host.c
+++ b/arch/x86/coco/sev/host.c
@@ -295,3 +295,46 @@ int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level)
 	return 0;
 }
 EXPORT_SYMBOL_GPL(snp_lookup_rmpentry);
+
+void sev_dump_rmpentry(u64 pfn)
+{
+	unsigned long pfn_end;
+	struct rmpentry e;
+	int level, ret;
+
+	ret = __snp_lookup_rmpentry(pfn, &e, &level);
+	if (ret) {
+		pr_info("Failed to read RMP entry for PFN 0x%llx, error %d\n", pfn, ret);
+		return;
+	}
+
+	if (rmpentry_assigned(&e)) {
+		pr_info("RMPEntry paddr 0x%llx: [high=0x%016llx low=0x%016llx]\n",
+			pfn << PAGE_SHIFT, e.high, e.low);
+		return;
+	}
+
+	/*
+	 * If the RMP entry at the faulting pfn was not assigned, then not sure
+	 * what caused the RMP violation. To get some useful debug information,
+	 * iterate through the entire 2MB region, and dump the RMP entries if
+	 * one of the bit in the RMP entry is set.
+	 */
+	pfn = pfn & ~(PTRS_PER_PMD - 1);
+	pfn_end = pfn + PTRS_PER_PMD;
+
+	while (pfn < pfn_end) {
+		ret = __snp_lookup_rmpentry(pfn, &e, &level);
+		if (ret) {
+			pr_info("Failed to read RMP entry for PFN 0x%llx\n", pfn);
+			pfn++;
+			continue;
+		}
+
+		if (e.low || e.high)
+			pr_info("RMPEntry paddr 0x%llx: [high=0x%016llx low=0x%016llx]\n",
+				pfn << PAGE_SHIFT, e.high, e.low);
+		pfn++;
+	}
+}
+EXPORT_SYMBOL_GPL(sev_dump_rmpentry);
diff --git a/arch/x86/include/asm/sev-host.h b/arch/x86/include/asm/sev-host.h
index 30d47e20081d..85cfe577155c 100644
--- a/arch/x86/include/asm/sev-host.h
+++ b/arch/x86/include/asm/sev-host.h
@@ -15,8 +15,10 @@
 
 #ifdef CONFIG_KVM_AMD_SEV
 int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level);
+void sev_dump_rmpentry(u64 pfn);
 #else
 static inline int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level) { return 0; }
+static inline void sev_dump_rmpentry(u64 pfn) {}
 #endif
 
 #endif
-- 
2.25.1