[PATCH RFC v7 23/64] x86/fault: Add support to dump RMP entry on fault

[Michael Roth <michael.roth@xxxxxxx>]

From: Brijesh Singh <brijesh.singh@xxxxxxx>

When SEV-SNP is enabled globally, a write from the host goes through the
RMP check. If the hardware encounters the check failure, then it raises
the #PF (with RMP set). Dump the RMP entry at the faulting pfn to help
the debug.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
 arch/x86/include/asm/sev.h |  2 ++
 arch/x86/kernel/sev.c      | 43 ++++++++++++++++++++++++++++++++++++++
 arch/x86/mm/fault.c        |  7 ++++++-
 3 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 4eeedcaca593..2916f4150ac7 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -215,6 +215,7 @@ int snp_lookup_rmpentry(u64 pfn, int *level);
 int psmash(u64 pfn);
 int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, int asid, bool immutable);
 int rmp_make_shared(u64 pfn, enum pg_level 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) { }
@@ -247,6 +248,7 @@ static inline int rmp_make_private(u64 pfn, u64 gpa, enum pg_level level, int as
 	return -ENODEV;
 }
 static inline int rmp_make_shared(u64 pfn, enum pg_level level) { return -ENODEV; }
+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 e2b38c3551be..1dd1b36bdfea 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2508,6 +2508,49 @@ 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 (!e) {
+		pr_info("failed to read RMP entry 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);
+		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 (!e)
+			return;
+
+		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.
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index ded53879f98d..f2b16dcfbd9a 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -536,6 +536,8 @@ static void show_ldttss(const struct desc_ptr *gdt, const char *name, u16 index)
 static void
 show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address)
 {
+	unsigned long pfn;
+
 	if (!oops_may_print())
 		return;
 
@@ -608,7 +610,10 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long ad
 		show_ldttss(&gdt, "TR", tr);
 	}
 
-	dump_pagetable(address);
+	pfn = dump_pagetable(address);
+
+	if (error_code & X86_PF_RMP)
+		sev_dump_rmpentry(pfn);
 }
 
 static noinline void
-- 
2.25.1