On Mon, Mar 13, 2023, Huang, Kai wrote: > On Fri, 2023-03-10 at 13:42 -0800, Sean Christopherson wrote: > > Check "this" CPU instead of the boot CPU when querying SVM support so that > > the per-CPU checks done during hardware enabling actually function as > > intended, i.e. will detect issues where SVM isn't support on all CPUs. > > > > Disable migration for the use from svm_init() mostly so that the standard > > accessors for the per-CPU data can be used without getting yelled at by > > CONFIG_DEBUG_PREEMPT=y sanity checks. Preventing the "disabled by BIOS" > > error message from reporting the wrong CPU is largely a bonus, as ensuring > > a stable CPU during module load is a non-goal for KVM. > > > > Link: https://lore.kernel.org/all/ZAdxNgv0M6P63odE@xxxxxxxxxx > > Cc: Kai Huang <kai.huang@xxxxxxxxx> > > Cc: Chao Gao <chao.gao@xxxxxxxxx> > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > > Should we add: > > Fixes: c82a5c5c53c5 ("KVM: x86: Do compatibility checks when onlining CPU") > > As that commit introduced using raw_smp_processor_id() to get CPU id in > kvm_is_svm_supported() and print the CPU id out in error message? My vote is to not to add a Fixes because using raw_smp_processor_id() and not disabling migration for module probe case was deliberate and is safe. I don't want to give the impression that the existing code is functionally broken. The only quirk is that the reporting could be misleading. That said, I'm not against adding a Fixes tag, because I certainly can't argue against the reporting being flawed. > > --- > > arch/x86/kvm/svm/svm.c | 25 +++++++++++++++++++------ > > 1 file changed, 19 insertions(+), 6 deletions(-) > > > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > > index 2934f185960d..f04b61c3d9d8 100644 > > --- a/arch/x86/kvm/svm/svm.c > > +++ b/arch/x86/kvm/svm/svm.c > > @@ -520,18 +520,20 @@ static void svm_init_osvw(struct kvm_vcpu *vcpu) > > vcpu->arch.osvw.status |= 1; > > } > > > > -static bool kvm_is_svm_supported(void) > > +static bool __kvm_is_svm_supported(void) > > { > > - int cpu = raw_smp_processor_id(); > > + int cpu = smp_processor_id(); > > Since we have made sure __kvm_is_svm_supported() is always performed on a stable > cpu, should we keep using raw_smp_processor_id()? � > > It is faster than smp_processor_id() when CONFIG_DEBUG_PREEMPT=y, but yes the > latter can help to catch bug. Most kernels with any amount of CONFIG_DEBUG_* options enabled are comically slow anyways, I much prefer having the sanity checks than the performance.
