On 18/09/2015 15:39, Igor Mammedov wrote:
> When INIT/SIPI sequence is sent to VCPU which before that
> was in use by OS, VMRUN might fail with:
>
> KVM: entry failed, hardware error 0xffffffff
> EAX=00000000 EBX=00000000 ECX=00000000 EDX=000006d3
> ESI=00000000 EDI=00000000 EBP=00000000 ESP=00000000
> EIP=00000000 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
> ES =0000 00000000 0000ffff 00009300
> CS =9a00 0009a000 0000ffff 00009a00
> [...]
> CR0=60000010 CR2=b6f3e000 CR3=01942000 CR4=000007e0
> [...]
> EFER=0000000000000000
>
> with corresponding SVM error:
> KVM: FAILED VMRUN WITH VMCB:
> [...]
> cpl: 0 efer: 0000000000001000
> cr0: 0000000080010010 cr2: 00007fd7fe85bf90
> cr3: 0000000187d0c000 cr4: 0000000000000020
> [...]
>
> What happens is that VCPU state right after offlinig:
> CR0: 0x80050033 EFER: 0xd01 CR4: 0x7e0
> -> long mode with CR3 pointing to longmode page tables
>
> and when VCPU gets INIT/SIPI following transition happens
> CR0: 0 -> 0x60000010 EFER: 0x0 CR4: 0x7e0
> -> paging disabled with stale CR3
>
> However SVM under the hood puts VCPU in Paged Real Mode*
> which effectively translates CR0 0x60000010 -> 80010010 after
>
> svm_vcpu_reset()
> -> init_vmcb()
> -> kvm_set_cr0()
> -> svm_set_cr0()
>
> but from kvm_set_cr0() perspective CR0: 0 -> 0x60000010
> only caching bits are changed and
> commit d81135a57aa6
> ("KVM: x86: do not reset mmu if CR0.CD and CR0.NW are changed")'
> regressed svm_vcpu_reset() which relied on MMU being reset.
>
> As result VMRUN after svm_vcpu_reset() tries to run
> VCPU in Paged Real Mode with stale MMU context (longmode page tables),
> which causes some AMD CPUs** to bail out with VMEXIT_INVALID.
>
> Fix issue by unconditionally resetting MMU context
> at init_vmcb() time.
>
> --
> * AMD64 Architecture Programmer’s Manual,
> Volume 2: System Programming, rev: 3.25
> 15.19 Paged Real Mode
> ** Opteron 1216
>
> Signed-off-by: Igor Mammedov <imammedo@xxxxxxxxxx>
> ---
> arch/x86/kvm/svm.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index fdb8cb6..89173af 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1264,6 +1264,7 @@ static void init_vmcb(struct vcpu_svm *svm, bool init_event)
> * It also updates the guest-visible cr0 value.
> */
> (void)kvm_set_cr0(&svm->vcpu, X86_CR0_NW | X86_CR0_CD | X86_CR0_ET);
> + kvm_mmu_reset_context(&svm->vcpu);
>
> save->cr4 = X86_CR4_PAE;
> /* rdx = ?? */
>
Thanks. Unfortunately I have just sent a pull request to Linus, but
I'll add
Fixes: d81135a57aa6
Cc: stable@xxxxxxxxxxxxxxx
and send it out next week.
Paolo
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