Re: [PATCH 01/11] x86/snp: drop support for SNP hotplug

[Tom Lendacky <thomas.lendacky@amd.com>]

On 3/2/26 13:13, Tycho Andersen wrote:
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> 
> From: "Tycho Andersen (AMD)" <tycho@kernel.org>
> 
> During an SNP_INIT(_EX), the SEV firmware checks that all CPUs have SNPEn
> 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.
> 
> Futher, there is a bug: SNP_INIT(_EX) require MFDM to be set in addition to
> SNPEn which the previous hotplug code did not do. Since
> k8_check_syscfg_dram_mod_en() enforces this be cleared, hotplug wouldn't
> work.
> 
> Drop the hotplug code. Collapse the __{mfd,snp}__enable() wrappers into
> their non-__ versions, since the cpu number argument is no longer needed.
> 
> Signed-off-by: Tycho Andersen (AMD) <tycho@kernel.org>

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>

> ---
>  arch/x86/virt/svm/sev.c | 24 ++++--------------------
>  1 file changed, 4 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
> index a4f3a364fb65..1446011c6337 100644
> --- a/arch/x86/virt/svm/sev.c
> +++ b/arch/x86/virt/svm/sev.c
> @@ -130,33 +130,26 @@ static unsigned long snp_nr_leaked_pages;
>  #undef pr_fmt
>  #define pr_fmt(fmt)    "SEV-SNP: " fmt
> 
> -static int __mfd_enable(unsigned int cpu)
> +static __init void mfd_enable(void *arg)
>  {
>         u64 val;
> 
>         if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
> -               return 0;
> +               return;
> 
>         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());
> -}
> -
> -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 +157,6 @@ 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 +539,6 @@ 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.
> --
> 2.53.0
>