linux-kernel - [PATCH] x86/sev: Apply RMP table fixups for kexec.

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Date: Tue, 12 Mar 2024 18:47:57 +0000
From: Ashish Kalra <Ashish.Kalra@....com>
To: <linux-tip-commits@...r.kernel.org>
CC: <bp@...en8.de>, <thomas.lendacky@....com>, <michael.roth@....com>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/sev: Apply RMP table fixups for kexec.

From: Ashish Kalra <ashish.kalra@....com>

RMP table start and end physical range may not be aligned to 2MB in
the e820 tables causing fatal RMP page faults during kexec boot when
new page allocations are done in the same 2MB page as the RMP table.
Check if RMP table start and end physical range in e820_table is not
aligned to 2MB and in that case use e820__range_update() to map this
range to reserved.

Override e820__memory_setup_default() to check and apply these RMP table
fixups in e820_table before e820_table is used to setup
e280_table_firmware and e820_table_kexec.

Fixes: c3b86e61b756 ("x86/cpufeatures: Enable/unmask SEV-SNP CPU feature")
Signed-off-by: Ashish Kalra <ashish.kalra@....com>
---
 arch/x86/virt/svm/sev.c | 52 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index cffe1157a90a..e0d7584df28f 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -65,6 +65,8 @@ static u64 probed_rmp_base, probed_rmp_size;
 static struct rmpentry *rmptable __ro_after_init;
 static u64 rmptable_max_pfn __ro_after_init;
 
+static char *__init snp_rmptable_e820_fixup(void);
+
 static LIST_HEAD(snp_leaked_pages_list);
 static DEFINE_SPINLOCK(snp_leaked_pages_list_lock);
 
@@ -160,9 +162,59 @@ bool snp_probe_rmptable_info(void)
 	pr_info("RMP table physical range [0x%016llx - 0x%016llx]\n",
 		probed_rmp_base, probed_rmp_base + probed_rmp_size - 1);
 
+	/*
+	 * Override e820__memory_setup_default() to do any RMP table fixups
+	 * for kexec if required.
+	 */
+	x86_init.resources.memory_setup = snp_rmptable_e820_fixup;
+
 	return true;
 }
 
+/*
+ * Override e820__memory_setup_default() to do any RMP table fixups
+ * in e820_table before e820_table_firmware and e820_table_kexec
+ * are setup.
+ */
+static char *__init snp_rmptable_e820_fixup(void)
+{
+	/* Populate e820_table from BIOS-supplied e820 map */
+	char *p =  e820__memory_setup_default();
+	u64 pa;
+
+	/*
+	 * RMP table start & end physical range may not be aligned to 2MB in the
+	 * e820 tables causing fatal RMP page faults during kexec boot when new
+	 * page allocations are done in the same 2MB page as the RMP table.
+	 * Check if RMP table start & end physical range in e820_table is not aligned
+	 * to 2MB and in that case use e820__range_update() to map this range to reserved,
+	 * e820__range_update() nicely handles partial range update and also
+	 * merges any consecutive ranges of the same type.
+	 * Need to override e820__memory_setup_default() to check and apply
+	 * fixups in e820_table before e820_table is used to setup
+	 * e280_table_firmware and e820_table_kexec.
+	 */
+	pa = probed_rmp_base;
+	if (!IS_ALIGNED(pa, PMD_SIZE)) {
+		pa = ALIGN_DOWN(pa, PMD_SIZE);
+		if (e820__mapped_any(pa, pa + PMD_SIZE, E820_TYPE_RAM)) {
+			pr_info("Reserving start of RMP table on a 2MB boundary [0x%016llx]\n", pa);
+			e820__range_update(pa, PMD_SIZE, E820_TYPE_RAM, E820_TYPE_RESERVED);
+		}
+	}
+
+	pa = probed_rmp_base + probed_rmp_size;
+	if (!IS_ALIGNED(pa, PMD_SIZE)) {
+		pa = ALIGN_DOWN(pa, PMD_SIZE);
+		if (e820__mapped_any(pa, pa + PMD_SIZE, E820_TYPE_RAM)) {
+			pr_info("Reserving end of RMP table on a 2MB boundary [0x%016llx]\n", pa);
+			e820__range_update(pa, PMD_SIZE, E820_TYPE_RAM, E820_TYPE_RESERVED);
+		}
+	}
+
+	return p;
+}
+
 /*
  * Do the necessary preparations which are verified by the firmware as
  * described in the SNP_INIT_EX firmware command description in the SNP
-- 
2.34.1