Re: [stable-4.14/4.15] KVM: x86: fix backward migration with async_PF

On Fri, Mar 9, 2018 at 3:43 PM, Paolo Bonzini pbonzini@redhat.com wrote:

On 09/03/2018 14:20, Jack Wang wrote:

...

From: Radim Krčmář rkrcmar@redhat.com

commit fe2a3027e74e40a3ece3a4c1e4e51403090a907a upstream.

Guests on new hypersiors might set KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT bit when enabling async_PF, but this bit is reserved on old hypervisors, which results in a failure upon migration.

To avoid breaking different cases, we are checking for CPUID feature bit before enabling the feature and nothing else.

Fixes: 52a5c155cf79 ("KVM: async_pf: Let guest support delivery of async_pf from guest mode") Cc: stable@vger.kernel.org Reviewed-by: Wanpeng Li wanpengli@tencent.com Reviewed-by: David Hildenbrand david@redhat.com Signed-off-by: Radim Krčmář rkrcmar@redhat.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com [jwang: port to 4.14] Signed-off-by: Jack Wang jinpu.wang@profitbricks.com

---

Documentation/virtual/kvm/cpuid.txt | 4 ++++ Documentation/virtual/kvm/msr.txt | 3 ++- arch/x86/include/uapi/asm/kvm_para.h | 1 + arch/x86/kernel/kvm.c | 8 ++++---- arch/x86/kvm/cpuid.c | 3 ++- 5 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt index 3c65feb..a81c97a 100644 --- a/Documentation/virtual/kvm/cpuid.txt +++ b/Documentation/virtual/kvm/cpuid.txt @@ -54,6 +54,10 @@ KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit || || before enabling paravirtualized || || spinlock support.

---

+KVM_FEATURE_ASYNC_PF_VMEXIT || 10 || paravirtualized async PF VM exit

•                               ||       || can be enabled by setting bit 2
  

•                               ||       || when writing to msr 0x4b564d02
  

+------------------------------------------------------------------------------ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side || || per-cpu warps are expected in || || kvmclock. diff --git a/Documentation/virtual/kvm/msr.txt b/Documentation/virtual/kvm/msr.txt index 1ebecc1..f3f0d57 100644 --- a/Documentation/virtual/kvm/msr.txt +++ b/Documentation/virtual/kvm/msr.txt @@ -170,7 +170,8 @@ MSR_KVM_ASYNC_PF_EN: 0x4b564d02 when asynchronous page faults are enabled on the vcpu 0 when disabled. Bit 1 is 1 if asynchronous page faults can be injected when vcpu is in cpl == 0. Bit 2 is 1 if asynchronous page faults

• are delivered to L1 as #PF vmexits.
  

• are delivered to L1 as #PF vmexits.  Bit 2 can be set only if
  

• KVM_FEATURE_ASYNC_PF_VMEXIT is present in CPUID.
  
  First 4 byte of 64 byte memory location will be written to by
  the hypervisor at the time of asynchronous page fault (APF)
  

diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h index 09cc064..989db88 100644 --- a/arch/x86/include/uapi/asm/kvm_para.h +++ b/arch/x86/include/uapi/asm/kvm_para.h @@ -25,6 +25,7 @@ #define KVM_FEATURE_STEAL_TIME 5 #define KVM_FEATURE_PV_EOI 6 #define KVM_FEATURE_PV_UNHALT 7 +#define KVM_FEATURE_ASYNC_PF_VMEXIT 10

/* The last 8 bits are used to indicate how to interpret the flags field

• in pvclock structure. If no bits are set, all flags are ignored.

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index b40ffbf..0a93e83b 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -341,10 +341,10 @@ static void kvm_guest_cpu_init(void) #endif pa |= KVM_ASYNC_PF_ENABLED;

•         /* Async page fault support for L1 hypervisor is optional */
  

•         if (wrmsr_safe(MSR_KVM_ASYNC_PF_EN,
  

•                 (pa | KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT) & 0xffffffff, pa >> 32) < 0)
  

•                 wrmsrl(MSR_KVM_ASYNC_PF_EN, pa);
  

•         if (kvm_para_has_feature(KVM_FEATURE_ASYNC_PF_VMEXIT))
  

•                 pa |= KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT;
  

•         wrmsrl(MSR_KVM_ASYNC_PF_EN, pa);
          __this_cpu_write(apf_reason.enabled, 1);
          printk(KERN_INFO"KVM setup async PF for cpu %d\n",
                 smp_processor_id());
  

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 13f5d42..4f544f2 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -597,7 +597,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, (1 << KVM_FEATURE_ASYNC_PF) | (1 << KVM_FEATURE_PV_EOI) | (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |

•                      (1 << KVM_FEATURE_PV_UNHALT);
  

•                      (1 << KVM_FEATURE_PV_UNHALT) |
  

•                      (1 << KVM_FEATURE_ASYNC_PF_VMEXIT);
  
          if (sched_info_on())
                  entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
  
  

Acked-by: Paolo Bonzini pbonzini@redhat.com

Thanks Jack!

Paolo

Thanks Paolo!

Jack