On 08/07/20 10:17, Wanpeng Li wrote:
> On Sat, 18 Apr 2020 at 00:39, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>> When a nested page fault is taken from an address that does not have
>> a memslot associated to it, kvm_mmu_do_page_fault returns RET_PF_EMULATE
>> (via mmu_set_spte) and kvm_mmu_page_fault then invokes svm_need_emulation_on_page_fault.
>>
>> The default answer there is to return false, but in this case this just
>> causes the page fault to be retried ad libitum. Since this is not a
>> fast path, and the only other case where it is taken is an erratum,
>> just stick a kvm_vcpu_gfn_to_memslot check in there to detect the
>> common case where the erratum is not happening.
>>
>> This fixes an infinite loop in the new set_memory_region_test.
>>
>> Fixes: 05d5a4863525 ("KVM: SVM: Workaround errata#1096 (insn_len maybe zero on SMAP violation)")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> ---
>> arch/x86/kvm/svm/svm.c | 7 +++++++
>> virt/kvm/kvm_main.c | 1 +
>> 2 files changed, 8 insertions(+)
>>
>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>> index a91e397d6750..c86f7278509b 100644
>> --- a/arch/x86/kvm/svm/svm.c
>> +++ b/arch/x86/kvm/svm/svm.c
>> @@ -3837,6 +3837,13 @@ static bool svm_need_emulation_on_page_fault(struct kvm_vcpu *vcpu)
>> bool smap = cr4 & X86_CR4_SMAP;
>> bool is_user = svm_get_cpl(vcpu) == 3;
>>
>> + /*
>> + * If RIP is invalid, go ahead with emulation which will cause an
>> + * internal error exit.
>> + */
>> + if (!kvm_vcpu_gfn_to_memslot(vcpu, kvm_rip_read(vcpu) >> PAGE_SHIFT))
>> + return true;
>> +
>> /*
>> * Detect and workaround Errata 1096 Fam_17h_00_0Fh.
>> *
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index e2f60e313c87..e7436d054305 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -1602,6 +1602,7 @@ struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn
>> {
>> return __gfn_to_memslot(kvm_vcpu_memslots(vcpu), gfn);
>> }
>> +EXPORT_SYMBOL_GPL(kvm_vcpu_gfn_to_memslot);
>
> This commit incurs the linux guest fails to boot once add --overcommit
> cpu-pm=on or not intercept hlt instruction, any thoughts?
Can you write a selftest?
Paolo
