Messages in this thread | | | From | Andy Lutomirski <> | Subject | Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions | Date | Tue, 12 Jan 2021 07:51:19 -0800 |
| |
> On Jan 12, 2021, at 7:46 AM, Bandan Das <bsd@redhat.com> wrote: > > Andy Lutomirski <luto@amacapital.net> writes: > ... >>>>>> #endif diff --git a/arch/x86/kvm/mmu/mmu.c >>>>>> b/arch/x86/kvm/mmu/mmu.c index 6d16481aa29d..c5c4aaf01a1a 100644 >>>>>> --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ >>>>>> -50,6 +50,7 @@ #include <asm/io.h> #include <asm/vmx.h> #include >>>>>> <asm/kvm_page_track.h> +#include <asm/e820/api.h> #include >>>>>> "trace.h" >>>>>> >>>>>> extern bool itlb_multihit_kvm_mitigation; @@ -5675,6 +5676,12 @@ >>>>>> void kvm_mmu_slot_set_dirty(struct kvm *kvm, } >>>>>> EXPORT_SYMBOL_GPL(kvm_mmu_slot_set_dirty); >>>>>> >>>>>> +bool kvm_is_host_reserved_region(u64 gpa) +{ + return >>>>>> e820__mbapped_raw_any(gpa-1, gpa+1, E820_TYPE_RESERVED); +} >>>>> While _e820__mapped_any()'s doc says '.. checks if any part of >>>>> the range <start,end> is mapped ..' it seems to me that the real >>>>> check is [start, end) so we should use 'gpa' instead of 'gpa-1', >>>>> no? >>>> Why do you need to check GPA at all? >>>> >>> To reduce the scope of the workaround. >>> >>> The errata only happens when you use one of SVM instructions in the >>> guest with EAX that happens to be inside one of the host reserved >>> memory regions (for example SMM). >> >> This code reduces the scope of the workaround at the cost of >> increasing the complexity of the workaround and adding a nonsensical >> coupling between KVM and host details and adding an export that really >> doesn’t deserve to be exported. >> >> Is there an actual concrete benefit to this check? > > Besides reducing the scope, my intention for the check was that we should > know if such exceptions occur for any other undiscovered reasons with other > memory types rather than hiding them under this workaround.
Ask AMD?
I would also believe that someone somewhere has a firmware that simply omits the problematic region instead of listing it as reserved.
> > Bandan > > >
| |