linux-kernel - Re: [PATCH v1 07/26] x86/fault: Add helper for dumping RMP entries

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Date: Wed, 10 Jan 2024 12:13:44 +0100
From: Borislav Petkov <bp@...en8.de>
To: Michael Roth <michael.roth@....com>
Cc: x86@...nel.org, kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
	linux-mm@...ck.org, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
	ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
	vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org,
	dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
	peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
	rientjes@...gle.com, tobin@....com, vbabka@...e.cz,
	kirill@...temov.name, ak@...ux.intel.com, tony.luck@...el.com,
	sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com,
	jarkko@...nel.org, ashish.kalra@....com, nikunj.dadhania@....com,
	pankaj.gupta@....com, liam.merwick@...cle.com, zhi.a.wang@...el.com,
	Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v1 07/26] x86/fault: Add helper for dumping RMP entries

On Sat, Dec 30, 2023 at 10:19:35AM -0600, Michael Roth wrote:
> +	while (pfn_current < pfn_end) {
> +		e = __snp_lookup_rmpentry(pfn_current, &level);
> +		if (IS_ERR(e)) {
> +			pfn_current++;
> +			continue;
> +		}
> +
> +		e_data = (u64 *)e;
> +		if (e_data[0] || e_data[1]) {
> +			pr_info("No assigned RMP entry for PFN 0x%llx, but the 2MB region contains populated RMP entries, e.g.: PFN 0x%llx: [high=0x%016llx low=0x%016llx]\n",
> +				pfn, pfn_current, e_data[1], e_data[0]);
> +			return;
> +		}
> +		pfn_current++;
> +	}
> +
> +	pr_info("No populated RMP entries in the 2MB region containing PFN 0x%llx\n",
> +		pfn);
> +}

Ok, I went and reworked this, see below.

Yes, I think it is important - at least in the beginning - to dump the
whole 2M PFN region for debugging purposes. If that output starts
becoming too unwieldy and overflowing terminals or log files, we'd
shorten it or put it behind a debug option or so.

Thx.

---
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index a8cf33b7da71..259a1dd655a7 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -35,16 +35,21 @@
  * Family 19h Model 01h, Rev B1 processor.
  */
 struct rmpentry {
-	u64	assigned	: 1,
-		pagesize	: 1,
-		immutable	: 1,
-		rsvd1		: 9,
-		gpa		: 39,
-		asid		: 10,
-		vmsa		: 1,
-		validated	: 1,
-		rsvd2		: 1;
-	u64 rsvd3;
+	union {
+		struct {
+			u64	assigned	: 1,
+				pagesize	: 1,
+				immutable	: 1,
+				rsvd1		: 9,
+				gpa		: 39,
+				asid		: 10,
+				vmsa		: 1,
+				validated	: 1,
+				rsvd2		: 1;
+		};
+		u64 lo;
+	};
+	u64 hi;
 } __packed;
 
 /*
@@ -272,22 +277,20 @@ EXPORT_SYMBOL_GPL(snp_lookup_rmpentry);
  */
 static void dump_rmpentry(u64 pfn)
 {
-	u64 pfn_current, pfn_end;
+	u64 pfn_i, pfn_end;
 	struct rmpentry *e;
-	u64 *e_data;
 	int level;
 
 	e = __snp_lookup_rmpentry(pfn, &level);
 	if (IS_ERR(e)) {
-		pr_info("Failed to read RMP entry for PFN 0x%llx, error %ld\n",
-			pfn, PTR_ERR(e));
+		pr_err("Error %ld reading RMP entry for PFN 0x%llx\n",
+			PTR_ERR(e), pfn);
 		return;
 	}
 
-	e_data = (u64 *)e;
 	if (e->assigned) {
-		pr_info("RMP entry for PFN 0x%llx: [high=0x%016llx low=0x%016llx]\n",
-			pfn, e_data[1], e_data[0]);
+		pr_info("PFN 0x%llx, RMP entry: [0x%016llx - 0x%016llx]\n",
+			pfn, e->lo, e->hi);
 		return;
 	}
 
@@ -299,27 +302,28 @@ static void dump_rmpentry(u64 pfn)
 	 * certain situations, such as when the PFN is being accessed via a 2MB
 	 * mapping in the host page table.
 	 */
-	pfn_current = ALIGN(pfn, PTRS_PER_PMD);
-	pfn_end = pfn_current + PTRS_PER_PMD;
+	pfn_i = ALIGN(pfn, PTRS_PER_PMD);
+	pfn_end = pfn_i + PTRS_PER_PMD;
 
-	while (pfn_current < pfn_end) {
-		e = __snp_lookup_rmpentry(pfn_current, &level);
+	pr_info("PFN 0x%llx unassigned, dumping the whole 2M PFN region: [0x%llx - 0x%llx]\n",
+		pfn, pfn_i, pfn_end);
+
+	while (pfn_i < pfn_end) {
+		e = __snp_lookup_rmpentry(pfn_i, &level);
 		if (IS_ERR(e)) {
-			pfn_current++;
+			pr_err("Error %ld reading RMP entry for PFN 0x%llx\n",
+				PTR_ERR(e), pfn_i);
+			pfn_i++;
 			continue;
 		}
 
-		e_data = (u64 *)e;
-		if (e_data[0] || e_data[1]) {
-			pr_info("No assigned RMP entry for PFN 0x%llx, but the 2MB region contains populated RMP entries, e.g.: PFN 0x%llx: [high=0x%016llx low=0x%016llx]\n",
-				pfn, pfn_current, e_data[1], e_data[0]);
-			return;
-		}
-		pfn_current++;
-	}
+		if (e->lo || e->hi)
+			pr_info("PFN: 0x%llx, [0x%016llx - 0x%016llx]\n", pfn_i, e->lo, e->hi);
+		else
+			pr_info("PFN: 0x%llx ...\n", pfn_i);
 
-	pr_info("No populated RMP entries in the 2MB region containing PFN 0x%llx\n",
-		pfn);
+		pfn_i++;
+	}
 }
 
 void snp_dump_hva_rmpentry(unsigned long hva)
@@ -339,4 +343,3 @@ void snp_dump_hva_rmpentry(unsigned long hva)
 
 	dump_rmpentry(pte_pfn(*pte));
 }
-EXPORT_SYMBOL_GPL(snp_dump_hva_rmpentry);

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette