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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@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://patch.msgid.link/20260324161301.1353976-4-tycho@kernel.org
master
Tycho Andersen (AMD) 2026-03-24 10:12:57 -06:00 committed by Borislav Petkov (AMD)
parent ca2ca373ec
commit b65546b14d
2 changed files with 21 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/include/asm/sev.h
View File

@ -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

22
arch/x86/virt/svm/sev.c
View File

@ -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