From 959d3f7565352fab844ae73a722631c5f615427f Mon Sep 17 00:00:00 2001 From: "Tycho Andersen (AMD)" Date: Mon, 9 Mar 2026 12:00:43 -0600 Subject: [PATCH] x86/virt/sev: Drop support for SNP hotplug During an SNP_INIT(_EX), the SEV firmware checks that all CPUs have the SNP syscfg bit set, and fails if they do not. As such, it does not make sense to have offline CPUs: the firmware will fail initialization because of the offlined ones that the kernel did not initialize. Further, there is a bug: during SNP_INIT(_EX) the firmware requires the MFDM syscfg bit to be set in addition to having SNP enabled, which the previous hotplug code did not do. Since k8_check_syscfg_dram_mod_en() enforces this be cleared, hotplug wouldn't work. Signed-off-by: Tycho Andersen (AMD) Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Tom Lendacky Link: https://patch.msgid.link/20260309180053.2389118-2-tycho@kernel.org --- arch/x86/virt/svm/sev.c | 34 ++++++---------------------------- 1 file changed, 6 insertions(+), 28 deletions(-) diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c index a4f3a364fb65..f404c609582c 100644 --- a/arch/x86/virt/svm/sev.c +++ b/arch/x86/virt/svm/sev.c @@ -130,33 +130,20 @@ static unsigned long snp_nr_leaked_pages; #undef pr_fmt #define pr_fmt(fmt) "SEV-SNP: " fmt -static int __mfd_enable(unsigned int cpu) -{ - u64 val; - - if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP)) - return 0; - - rdmsrq(MSR_AMD64_SYSCFG, val); - - val |= MSR_AMD64_SYSCFG_MFDM; - - wrmsrq(MSR_AMD64_SYSCFG, val); - - return 0; -} - static __init void mfd_enable(void *arg) { - __mfd_enable(smp_processor_id()); + if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP)) + return; + + msr_set_bit(MSR_AMD64_SYSCFG, MSR_AMD64_SYSCFG_MFDM_BIT); } -static int __snp_enable(unsigned int cpu) +static __init void snp_enable(void *arg) { u64 val; if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP)) - return 0; + return; rdmsrq(MSR_AMD64_SYSCFG, val); @@ -164,13 +151,6 @@ static int __snp_enable(unsigned int cpu) val |= MSR_AMD64_SYSCFG_SNP_VMPL_EN; wrmsrq(MSR_AMD64_SYSCFG, val); - - return 0; -} - -static __init void snp_enable(void *arg) -{ - __snp_enable(smp_processor_id()); } static void __init __snp_fixup_e820_tables(u64 pa) @@ -553,8 +533,6 @@ int __init snp_rmptable_init(void) on_each_cpu(snp_enable, NULL, 1); skip_enable: - cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/rmptable_init:online", __snp_enable, NULL); - /* * Setting crash_kexec_post_notifiers to 'true' to ensure that SNP panic * notifier is invoked to do SNP IOMMU shutdown before kdump.