Re: [PATCH v2] x86/cpu: Reinitialize IA32_FEAT_CTL MSR on BSP during wakeup

[Paolo Bonzini]

On 25/06/20 14:06, Rafael J. Wysocki wrote:
> On Mon, Jun 8, 2020 at 7:49 PM Sean Christopherson
> <sean.j.christopherson@xxxxxxxxx> wrote:
>>
>> Reinitialize IA32_FEAT_CTL on the BSP during wakeup to handle the case
>> where firmware doesn't initialize or save/restore across S3.  This fixes
>> a bug where IA32_FEAT_CTL is left uninitialized and results in VMXON
>> taking a #GP due to VMX not being fully enabled, i.e. breaks KVM.
>>
>> Use init_ia32_feat_ctl() to "restore" IA32_FEAT_CTL as it already deals
>> with the case where the MSR is locked, and because APs already redo
>> init_ia32_feat_ctl() during suspend by virtue of the SMP boot flow being
>> used to reinitialize APs upon wakeup.  Do the call in the early wakeup
>> flow to avoid dependencies in the syscore_ops chain, e.g. simply adding
>> a resume hook is not guaranteed to work, as KVM does VMXON in its own
>> resume hook, kvm_resume(), when KVM has active guests.
>>
>> Reported-by: Brad Campbell <lists2009@xxxxxxxxxxxxxxx>
>> Tested-by: Brad Campbell <lists2009@xxxxxxxxxxxxxxx>
>> Reviewed-by: Liam Merwick <liam.merwick@xxxxxxxxxx>
>> Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> Cc: kvm@xxxxxxxxxxxxxxx
>> Cc: stable@xxxxxxxxxxxxxxx # v5.6
>> Fixes: 21bd3467a58e ("KVM: VMX: Drop initialization of IA32_FEAT_CTL MSR")
>> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> 
> Given the regression fix nature of this patch, is it being taken care
> of by anyone (tip in particular) already?

I was waiting for tip to pick it up, but I can as well with an Acked-by
(KVM is broken by the patch but there's nothing KVM specific in it).

Paolo

>> ---
>>
>> v2:
>>   - Collect Reviewed/Tested tags. [Brad, Liam, Maxim].
>>   - Include asm/cpu.h to fix Zhaoxin and Centaur builds. [Brad, LKP]
>>   - Add Cc to stable. [Liam]
>>
>>  arch/x86/include/asm/cpu.h    | 5 +++++
>>  arch/x86/kernel/cpu/centaur.c | 1 +
>>  arch/x86/kernel/cpu/cpu.h     | 4 ----
>>  arch/x86/kernel/cpu/zhaoxin.c | 1 +
>>  arch/x86/power/cpu.c          | 6 ++++++
>>  5 files changed, 13 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
>> index dd17c2da1af5..da78ccbd493b 100644
>> --- a/arch/x86/include/asm/cpu.h
>> +++ b/arch/x86/include/asm/cpu.h
>> @@ -58,4 +58,9 @@ static inline bool handle_guest_split_lock(unsigned long ip)
>>         return false;
>>  }
>>  #endif
>> +#ifdef CONFIG_IA32_FEAT_CTL
>> +void init_ia32_feat_ctl(struct cpuinfo_x86 *c);
>> +#else
>> +static inline void init_ia32_feat_ctl(struct cpuinfo_x86 *c) {}
>> +#endif
>>  #endif /* _ASM_X86_CPU_H */
>> diff --git a/arch/x86/kernel/cpu/centaur.c b/arch/x86/kernel/cpu/centaur.c
>> index 426792565d86..c5cf336e5077 100644
>> --- a/arch/x86/kernel/cpu/centaur.c
>> +++ b/arch/x86/kernel/cpu/centaur.c
>> @@ -3,6 +3,7 @@
>>  #include <linux/sched.h>
>>  #include <linux/sched/clock.h>
>>
>> +#include <asm/cpu.h>
>>  #include <asm/cpufeature.h>
>>  #include <asm/e820/api.h>
>>  #include <asm/mtrr.h>
>> diff --git a/arch/x86/kernel/cpu/cpu.h b/arch/x86/kernel/cpu/cpu.h
>> index 37fdefd14f28..38ab6e115eac 100644
>> --- a/arch/x86/kernel/cpu/cpu.h
>> +++ b/arch/x86/kernel/cpu/cpu.h
>> @@ -80,8 +80,4 @@ extern void x86_spec_ctrl_setup_ap(void);
>>
>>  extern u64 x86_read_arch_cap_msr(void);
>>
>> -#ifdef CONFIG_IA32_FEAT_CTL
>> -void init_ia32_feat_ctl(struct cpuinfo_x86 *c);
>> -#endif
>> -
>>  #endif /* ARCH_X86_CPU_H */
>> diff --git a/arch/x86/kernel/cpu/zhaoxin.c b/arch/x86/kernel/cpu/zhaoxin.c
>> index df1358ba622b..05fa4ef63490 100644
>> --- a/arch/x86/kernel/cpu/zhaoxin.c
>> +++ b/arch/x86/kernel/cpu/zhaoxin.c
>> @@ -2,6 +2,7 @@
>>  #include <linux/sched.h>
>>  #include <linux/sched/clock.h>
>>
>> +#include <asm/cpu.h>
>>  #include <asm/cpufeature.h>
>>
>>  #include "cpu.h"
>> diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
>> index aaff9ed7ff45..b0d3c5ca6d80 100644
>> --- a/arch/x86/power/cpu.c
>> +++ b/arch/x86/power/cpu.c
>> @@ -193,6 +193,8 @@ static void fix_processor_context(void)
>>   */
>>  static void notrace __restore_processor_state(struct saved_context *ctxt)
>>  {
>> +       struct cpuinfo_x86 *c;
>> +
>>         if (ctxt->misc_enable_saved)
>>                 wrmsrl(MSR_IA32_MISC_ENABLE, ctxt->misc_enable);
>>         /*
>> @@ -263,6 +265,10 @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
>>         mtrr_bp_restore();
>>         perf_restore_debug_store();
>>         msr_restore_context(ctxt);
>> +
>> +       c = &cpu_data(smp_processor_id());
>> +       if (cpu_has(c, X86_FEATURE_MSR_IA32_FEAT_CTL))
>> +               init_ia32_feat_ctl(c);
>>  }
>>
>>  /* Needed by apm.c */
>> --
>> 2.26.0
>>
>