Messages in this thread | | | Subject | Re: [PATCH] x86/pkeys: Manually set X86_FEATURE_OSPKE to preserve existing changes | From | Jacob Keller <> | Date | Wed, 26 Feb 2020 16:16:13 -0800 |
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On 2/26/2020 3:16 PM, Sean Christopherson wrote: > Explicitly set X86_FEATURE_OSPKE via set_cpu_cap() instead of calling > get_cpu_cap() to pull the feature bit from CPUID after enabling CR4.PKE. > Invoking get_cpu_cap() effectively wipes out any {set,clear}_cpu_cap() > changes that were made between this_cpu->c_init() and setup_pku(), as > all non-synthetic feature words are reinitialized from the CPU's CPUID > values. > > Blasting away capability updates manifests most visibility when running > on a VMX capable CPU, but with VMX disabled by BIOS. To indicate that > VMX is disabled, init_ia32_feat_ctl() clears X86_FEATURE_VMX, using > clear_cpu_cap() instead of setup_clear_cpu_cap() so that KVM can report > which CPU is misconfigured (KVM needs to probe every CPU anyways). > Restoring X86_FEATURE_VMX from CPUID causes KVM to think VMX is enabled, > ultimately leading to an unexpected #GP when KVM attempts to do VMXON. > > Arguably, init_ia32_feat_ctl() should use setup_clear_cpu_cap() and let > KVM figure out a different way to report the misconfigured CPU, but VMX > is not the only feature bit that is affected, i.e. there is precedent > that tweaking feature bits via {set,clear}_cpu_cap() after ->c_init() > is expected to work. Most notably, x86_init_rdrand()'s clearing of > X86_FEATURE_RDRAND when RDRAND malfunctions is also overwritten. > > Fixes: 0697694564c8 ("x86/mm/pkeys: Actually enable Memory Protection Keys in the CPU") > Cc: stable@vger.kernel.org > Cc: Dave Hansen <dave.hansen@linux.intel.com> > Reported-by: Jacob Keller <jacob.e.keller@intel.com> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> > --- >
I tested this and it resolves my report! Thanks for a timely fix.
I agree with the analysis. Perhaps it would make sense in the long term to find a solution where get_cpu_cap can remember what was cleared for each CPU and restore those? It already does this using the global variables...
Thanks, Jake
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