[tip: x86/sev] x86/sev: Map only the RMP table entries instead of the full RMP range

["tip-bot2 for Tom Lendacky" <tip-bot2@linutronix.de>]

The following commit has been merged into the x86/sev branch of tip:

Commit-ID:     ac517965a5a12d685f1e7a7f77e64503167f87d5
Gitweb:        https://git.kernel.org/tip/ac517965a5a12d685f1e7a7f77e64503167f87d5
Author:        Tom Lendacky <thomas.lendacky@amd.com>
AuthorDate:    Mon, 02 Dec 2024 14:50:50 -06:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Sat, 14 Dec 2024 11:39:02 +01:00

x86/sev: Map only the RMP table entries instead of the full RMP range

In preparation for support of a segmented RMP table, map only the RMP
table entries. The RMP bookkeeping area is only ever accessed when
first enabling SNP and does not need to remain mapped. To accomplish
this, split the initialization of the RMP bookkeeping area and the
initialization of the RMP entry area. The RMP bookkeeping area will be
mapped only while it is being initialized.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Nikunj A Dadhania <nikunj@amd.com>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Reviewed-by: Ashish Kalra <ashish.kalra@amd.com>
Link: https://lore.kernel.org/r/22f179998d319834f49c13a8c01187fbf0fd308d.1733172653.git.thomas.lendacky@amd.com
---
 arch/x86/virt/svm/sev.c | 36 +++++++++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 5 deletions(-)

diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 0df3789..2899c2e 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -173,6 +173,23 @@ void __init snp_fixup_e820_tables(void)
 	__snp_fixup_e820_tables(probed_rmp_base + probed_rmp_size);
 }
 
+static bool __init clear_rmptable_bookkeeping(void)
+{
+	void *bk;
+
+	bk = memremap(probed_rmp_base, RMPTABLE_CPU_BOOKKEEPING_SZ, MEMREMAP_WB);
+	if (!bk) {
+		pr_err("Failed to map RMP bookkeeping area\n");
+		return false;
+	}
+
+	memset(bk, 0, RMPTABLE_CPU_BOOKKEEPING_SZ);
+
+	memunmap(bk);
+
+	return true;
+}
+
 /*
  * Do the necessary preparations which are verified by the firmware as
  * described in the SNP_INIT_EX firmware command description in the SNP
@@ -210,12 +227,17 @@ static int __init snp_rmptable_init(void)
 		goto nosnp;
 	}
 
-	rmptable_start = memremap(probed_rmp_base, probed_rmp_size, MEMREMAP_WB);
+	/* Map only the RMP entries */
+	rmptable_start = memremap(probed_rmp_base + RMPTABLE_CPU_BOOKKEEPING_SZ,
+				  probed_rmp_size - RMPTABLE_CPU_BOOKKEEPING_SZ,
+				  MEMREMAP_WB);
 	if (!rmptable_start) {
 		pr_err("Failed to map RMP table\n");
 		goto nosnp;
 	}
 
+	rmptable_size = probed_rmp_size - RMPTABLE_CPU_BOOKKEEPING_SZ;
+
 	/*
 	 * Check if SEV-SNP is already enabled, this can happen in case of
 	 * kexec boot.
@@ -224,7 +246,14 @@ static int __init snp_rmptable_init(void)
 	if (val & MSR_AMD64_SYSCFG_SNP_EN)
 		goto skip_enable;
 
-	memset(rmptable_start, 0, probed_rmp_size);
+	/* Zero out the RMP bookkeeping area */
+	if (!clear_rmptable_bookkeeping()) {
+		memunmap(rmptable_start);
+		goto nosnp;
+	}
+
+	/* Zero out the RMP entries */
+	memset(rmptable_start, 0, rmptable_size);
 
 	/* Flush the caches to ensure that data is written before SNP is enabled. */
 	wbinvd_on_all_cpus();
@@ -235,9 +264,6 @@ static int __init snp_rmptable_init(void)
 	on_each_cpu(snp_enable, NULL, 1);
 
 skip_enable:
-	rmptable_start += RMPTABLE_CPU_BOOKKEEPING_SZ;
-	rmptable_size = probed_rmp_size - RMPTABLE_CPU_BOOKKEEPING_SZ;
-
 	rmptable = (struct rmpentry_raw *)rmptable_start;
 	rmptable_max_pfn = rmptable_size / sizeof(struct rmpentry_raw) - 1;