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Drop cpus_read_lock()/cpus_read_unlock() here. >> The RMPOPT setup and cleanup added later are introduced after this patch >> and never take the lock for the same reason. > > Why do I even bother writing it? > > "do ... not talk about future patches because git history is not always > linear" Will drop the future patch reference from the commit log. > >> Suggested-by: Thomas Lendacky >> Suggested-by: Borislav Petkov (AMD) >> Signed-off-by: Ashish Kalra >> --- >> arch/x86/virt/svm/sev.c | 39 +++++++++++++++++++++++++++++---------- >> 1 file changed, 29 insertions(+), 10 deletions(-) >> >> diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c >> index cff285d8ad8e..e2f69fba0938 100644 >> --- a/arch/x86/virt/svm/sev.c >> +++ b/arch/x86/virt/svm/sev.c >> @@ -513,7 +513,6 @@ static void clear_hsave_pa(void *arg) >> >> int snp_prepare(void) >> { >> - int ret; >> u64 val; >> >> /* >> @@ -526,14 +525,21 @@ int snp_prepare(void) >> >> clear_rmp(); >> >> - cpus_read_lock(); >> + /* >> + * Disable CPU hotplug before enabling SNP: no CPU may come online >> + * without SnpEn while SNP is active, and none may go offline during >> + * enable. This keeps cpu_online_mask stable for the check and the >> + * on_each_cpu() calls below, so cpus_read_lock() is not needed. It is >> + * re-enabled in snp_shutdown() once the firmware disables SNP. >> + */ >> + cpu_hotplug_disable(); > > No need for too much splainin' and besides, that comment'll grow out-of-whack > sooner than you think: > Will trim the comment. > diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c > index e2f69fba0938..731ea25fba37 100644 > --- a/arch/x86/virt/svm/sev.c > +++ b/arch/x86/virt/svm/sev.c > @@ -528,9 +528,7 @@ int snp_prepare(void) > /* > * Disable CPU hotplug before enabling SNP: no CPU may come online > * without SnpEn while SNP is active, and none may go offline during > - * enable. This keeps cpu_online_mask stable for the check and the > - * on_each_cpu() calls below, so cpus_read_lock() is not needed. It is > - * re-enabled in snp_shutdown() once the firmware disables SNP. > + * enable. > */ > cpu_hotplug_disable(); > >> if (!cpumask_equal(cpu_online_mask, cpu_present_mask)) { >> - ret = -EOPNOTSUPP; >> + cpu_hotplug_enable(); >> pr_warn("SNP init failed: not all CPUs online. (%*pbl online <-> %*pbl present masks).\n", >> cpumask_pr_args(cpu_online_mask), >> cpumask_pr_args(cpu_present_mask)); >> - goto unlock; >> + return -EOPNOTSUPP; >> } >> >> wbinvd_on_all_cpus(); >> @@ -548,12 +554,7 @@ int snp_prepare(void) >> /* SNP_INIT requires MSR_VM_HSAVE_PA to be cleared on all CPUs. */ >> on_each_cpu(clear_hsave_pa, NULL, 1); >> >> - ret = 0; >> - >> -unlock: >> - cpus_read_unlock(); >> - >> - return ret; >> + return 0; >> } >> EXPORT_SYMBOL_FOR_MODULES(snp_prepare, "ccp"); >> >> @@ -565,6 +566,13 @@ void snp_shutdown(void) >> if (syscfg & MSR_AMD64_SYSCFG_SNP_EN) >> return; >> >> + /* >> + * The firmware has disabled SNP (SnpEn is clear), so re-enable CPU >> + * hotplug. A legacy SNP shutdown returns above with SnpEn still set and >> + * leaves hotplug disabled. >> + */ >> + cpu_hotplug_enable(); > > What happens if CPUs get offlined here after hotplug has been enabled and... > >> clear_rmp(); >> on_each_cpu(mfd_reconfigure, NULL, 1); > > ... they miss the mfd_reconfigure()? > >> } > Yes, re-enable should happens last in snp_shutdown() (after clear_rmp()/mfd_reconfigure()). Thanks, Ashish