[tip: x86/sev] x86/sev: Create snp_shutdown()

[tip-bot2 for Tycho Andersen (AMD)]

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

Commit-ID:     b65546b14d273dde2a56c0313da36a6aeb5c3f32
Gitweb:        https://git.kernel.org/tip/b65546b14d273dde2a56c0313da36a6aeb5c3f32
Author:        Tycho Andersen (AMD) <tycho@xxxxxxxxxx>
AuthorDate:    Tue, 24 Mar 2026 10:12:57 -06:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Sun, 29 Mar 2026 12:15:17 +02:00

x86/sev: Create snp_shutdown()

After SNP_SHUTDOWN, two things should be done:

1. clear the RMP table
2. disable MFDM to prevent the FW_WARN in k8_check_syscfg_dram_mod_en() in
   the event of a kexec

Create and export to the CCP driver a function that does them.

Also change the MFDM helper to allow for disabling the bit, since the SNP x86
shutdown path needs to disable MFDM.

The comment for k8_check_syscfg_dram_mod_en() notes, the "BIOS" is supposed
clear it, or the kernel in the case of module unload and shutdown followed by
kexec.

Signed-off-by: Tycho Andersen (AMD) <tycho@xxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Link: https://patch.msgid.link/20260324161301.1353976-4-tycho@xxxxxxxxxx
---
 arch/x86/include/asm/sev.h |  2 ++
 arch/x86/virt/svm/sev.c    | 22 +++++++++++++++++++---
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 2140e26..09e605c 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -662,6 +662,7 @@ static inline void snp_leak_pages(u64 pfn, unsigned int pages)
 	__snp_leak_pages(pfn, pages, true);
 }
 void snp_prepare(void);
+void snp_shutdown(void);
 #else
 static inline bool snp_probe_rmptable_info(void) { return false; }
 static inline int snp_rmptable_init(void) { return -ENOSYS; }
@@ -679,6 +680,7 @@ static inline void snp_leak_pages(u64 pfn, unsigned int npages) {}
 static inline void kdump_sev_callback(void) { }
 static inline void snp_fixup_e820_tables(void) {}
 static inline void snp_prepare(void) {}
+static inline void snp_shutdown(void) {}
 #endif
 
 #endif
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index ccec529..3b2273d 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -132,12 +132,15 @@ static unsigned long snp_nr_leaked_pages;
 #undef pr_fmt
 #define pr_fmt(fmt)	"SEV-SNP: " fmt
 
-static void mfd_enable(void *arg)
+static void mfd_reconfigure(void *arg)
 {
 	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
 		return;
 
-	msr_set_bit(MSR_AMD64_SYSCFG, MSR_AMD64_SYSCFG_MFDM_BIT);
+	if (arg)
+		msr_set_bit(MSR_AMD64_SYSCFG, MSR_AMD64_SYSCFG_MFDM_BIT);
+	else
+		msr_clear_bit(MSR_AMD64_SYSCFG, MSR_AMD64_SYSCFG_MFDM_BIT);
 }
 
 static void snp_enable(void *arg)
@@ -523,13 +526,26 @@ void snp_prepare(void)
 	 * MtrrFixDramModEn is not shared between threads on a core,
 	 * therefore it must be set on all CPUs prior to enabling SNP.
 	 */
-	on_each_cpu(mfd_enable, NULL, 1);
+	on_each_cpu(mfd_reconfigure, (void *)1, 1);
 	on_each_cpu(snp_enable, NULL, 1);
 
 	cpus_read_unlock();
 }
 EXPORT_SYMBOL_FOR_MODULES(snp_prepare, "ccp");
 
+void snp_shutdown(void)
+{
+	u64 syscfg;
+
+	rdmsrq(MSR_AMD64_SYSCFG, syscfg);
+	if (syscfg & MSR_AMD64_SYSCFG_SNP_EN)
+		return;
+
+	clear_rmp();
+	on_each_cpu(mfd_reconfigure, NULL, 1);
+}
+EXPORT_SYMBOL_FOR_MODULES(snp_shutdown, "ccp");
+
 /*
  * Do the necessary preparations which are verified by the firmware as
  * described in the SNP_INIT_EX firmware command description in the SNP