Commit fe2a3027 authored by Radim Krčmář's avatar Radim Krčmář Committed by Paolo Bonzini
Browse files

KVM: x86: fix backward migration with async_PF 



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: 52a5c155 ("KVM: async_pf: Let guest support delivery of async_pf from guest mode")
Cc: <stable@vger.kernel.org>
Reviewed-by: default avatarWanpeng Li <wanpengli@tencent.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent f75e4924

Documentation/virtual/kvm/cpuid.txt

+4 −0
Original line number Diff line number Diff line
@@ -58,6 +58,10 @@ KVM_FEATURE_PV_TLB_FLUSH || 9 || guest checks this feature bit 
                                   ||       || before enabling paravirtualized

                                   ||       || tlb flush.

------------------------------------------------------------------------------

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.

Documentation/virtual/kvm/msr.txt

+2 −1
Original line number Diff line number Diff line
@@ -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)

arch/x86/include/uapi/asm/kvm_para.h

+1 −0
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ 
#define KVM_FEATURE_PV_EOI		6

#define KVM_FEATURE_PV_UNHALT		7

#define KVM_FEATURE_PV_TLB_FLUSH	9

#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.

arch/x86/kernel/kvm.c

+4 −4
Original line number Diff line number Diff line
@@ -341,9 +341,9 @@ 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)

		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",

arch/x86/kvm/cpuid.c

+2 −1
Original line number Diff line number Diff line
@@ -607,7 +607,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, 
			     (1 << KVM_FEATURE_PV_EOI) |

			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |

			     (1 << KVM_FEATURE_PV_UNHALT) |

			     (1 << KVM_FEATURE_PV_TLB_FLUSH);

			     (1 << KVM_FEATURE_PV_TLB_FLUSH) |

			     (1 << KVM_FEATURE_ASYNC_PF_VMEXIT);



		if (sched_info_on())

			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);

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