linux-kernel - [RFC Part2 PATCH 06/30] x86/fault: dump the RMP entry on #PF

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Date:   Wed, 24 Mar 2021 12:04:12 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        linux-crypto@...r.kernel.org
Cc:     ak@...ux.intel.com, herbert@...dor.apana.org.au,
        Brijesh Singh <brijesh.singh@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Joerg Roedel <jroedel@...e.de>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        David Rientjes <rientjes@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: [RFC Part2 PATCH 06/30] x86/fault: dump the RMP entry on #PF

If hardware detects an RMP violation, it will raise a page-fault exception
with the RMP bit set. To help the debug, dump the RMP entry of the faulting
address.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Joerg Roedel <jroedel@...e.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Tony Luck <tony.luck@...el.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Sean Christopherson <seanjc@...gle.com>
Cc: x86@...nel.org
Cc: kvm@...r.kernel.org
Signed-off-by: Brijesh Singh <brijesh.singh@....com>
---
 arch/x86/mm/fault.c | 75 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index f39b551f89a6..7605e06a6dd9 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -31,6 +31,7 @@
 #include <asm/pgtable_areas.h>		/* VMALLOC_START, ...		*/
 #include <asm/kvm_para.h>		/* kvm_handle_async_pf		*/
 #include <asm/vdso.h>			/* fixup_vdso_exception()	*/
+#include <asm/sev-snp.h>		/* lookup_rmpentry ...		*/
 
 #define CREATE_TRACE_POINTS
 #include <asm/trace/exceptions.h>
@@ -147,6 +148,76 @@ is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
 DEFINE_SPINLOCK(pgd_lock);
 LIST_HEAD(pgd_list);
 
+static void dump_rmpentry(struct page *page, rmpentry_t *e)
+{
+	unsigned long paddr = page_to_pfn(page) << PAGE_SHIFT;
+
+	pr_alert("RMPEntry paddr 0x%lx [assigned=%d immutable=%d pagesize=%d gpa=0x%lx asid=%d "
+		"vmsa=%d validated=%d]\n", paddr, rmpentry_assigned(e), rmpentry_immutable(e),
+		rmpentry_pagesize(e), rmpentry_gpa(e), rmpentry_asid(e), rmpentry_vmsa(e),
+		rmpentry_validated(e));
+	pr_alert("RMPEntry paddr 0x%lx %016llx %016llx\n", paddr, e->high, e->low);
+}
+
+static void show_rmpentry(unsigned long address)
+{
+	struct page *page = virt_to_page(address);
+	rmpentry_t *entry, *large_entry;
+	int level, rmp_level;
+	pgd_t *pgd;
+	pte_t *pte;
+
+	/* Get the RMP entry for the fault address */
+	entry = lookup_page_in_rmptable(page, &rmp_level);
+	if (!entry) {
+		pr_alert("SEV-SNP: failed to read RMP entry for address 0x%lx\n", address);
+		return;
+	}
+
+	dump_rmpentry(page, entry);
+
+	/*
+	 * If fault occurred during the large page walk, dump the RMP entry at base of 2MB page.
+	 */
+	pgd = __va(read_cr3_pa());
+	pgd += pgd_index(address);
+	pte = lookup_address_in_pgd(pgd, address, &level);
+	if ((level > PG_LEVEL_4K) && (!IS_ALIGNED(address, PMD_SIZE))) {
+		address = address & PMD_MASK;
+		large_entry = lookup_page_in_rmptable(virt_to_page(address), &rmp_level);
+		if (!large_entry) {
+			pr_alert("SEV-SNP: failed to read large RMP entry 0x%lx\n",
+				address & PMD_MASK);
+			return;
+		}
+
+		dump_rmpentry(virt_to_page(address), large_entry);
+	}
+
+	/*
+	 * If the RMP entry at the faulting address was not assigned, then dump may not provide
+	 * any 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.
+	 */
+	if (!rmpentry_assigned(entry)) {
+		unsigned long start, end;
+
+		start = address & PMD_MASK;
+		end = start + PMD_SIZE;
+
+		for (; start < end; start += PAGE_SIZE) {
+			entry = lookup_page_in_rmptable(virt_to_page(start), &rmp_level);
+			if (!entry)
+				return;
+
+			/* If any of the bits in RMP entry is set then dump it */
+			if (entry->high || entry->low)
+				pr_alert("RMPEntry paddr %lx: %016llx %016llx\n",
+					page_to_pfn(page) << PAGE_SHIFT, entry->high, entry->low);
+		}
+	}
+}
+
 #ifdef CONFIG_X86_32
 static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
 {
@@ -580,6 +651,10 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long ad
 	}
 
 	dump_pagetable(address);
+
+	if (error_code & X86_PF_RMP)
+		show_rmpentry(address);
+
 }
 
 static noinline void
-- 
2.17.1