[PATCH RFC v8 13/56] x86/fault: Add helper for dumping RMP entries

[Michael Roth]

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/include/asm/sev.h |  2 ++
 arch/x86/kernel/sev.c      | 48 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 8d3ce2ad27da..edbb7fa488af 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -198,6 +198,7 @@ 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);
+void sev_dump_rmpentry(u64 pfn);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
@@ -223,6 +224,7 @@ 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; }
+static inline void sev_dump_rmpentry(u64 pfn) {}
 #endif
 
 #endif
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index a063c1b98034..a01741c4a1b8 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2504,6 +2504,54 @@ static struct rmpentry *__snp_lookup_rmpentry(u64 pfn, int *level)
 	return entry;
 }
 
+void sev_dump_rmpentry(u64 pfn)
+{
+	unsigned long pfn_end;
+	struct rmpentry *e;
+	int level;
+
+	e = __snp_lookup_rmpentry(pfn, &level);
+	if (IS_ERR(e)) {
+		pr_info("Failed to read RMP entry for PFN 0x%llx\n", pfn);
+		return;
+	}
+
+	if (rmpentry_assigned(e)) {
+		pr_info("RMPEntry paddr 0x%llx [assigned=%d immutable=%d pagesize=%d gpa=0x%lx asid=%d vmsa=%d validated=%d]\n",
+			pfn << PAGE_SHIFT, rmpentry_assigned(e), e->info.immutable,
+			rmpentry_pagesize(e), (unsigned long)e->info.gpa, e->info.asid,
+			e->info.vmsa, e->info.validated);
+
+		/* Dump all the non-zero entries if debug enabled */
+		if (!sev_cfg.debug)
+			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) {
+		e = __snp_lookup_rmpentry(pfn, &level);
+		if (IS_ERR(e)) {
+			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);
+
 /*
  * 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.
-- 
2.25.1