19.06.2021 03:54, Sean Christopherson пишет:
On Sat, Jun 19, 2021, stsp wrote:
19.06.2021 01:32, Sean Christopherson пишет:
Argh! Check out this gem:
/*
* Fix the "Accessed" bit in AR field of segment registers for older
* qemu binaries.
* IA32 arch specifies that at the time of processor reset the
* "Accessed" bit in the AR field of segment registers is 1. And qemu
* is setting it to 0 in the userland code. This causes invalid guest
* state vmexit when "unrestricted guest" mode is turned on.
* Fix for this setup issue in cpu_reset is being pushed in the qemu
* tree. Newer qemu binaries with that qemu fix would not need this
* kvm hack.
*/
if (is_unrestricted_guest(vcpu) && (seg != VCPU_SREG_LDTR))
var->type |= 0x1; /* Accessed */
KVM fixes up segs when unrestricted guest is enabled, but otherwise leaves 'em
be, presumably because it has the emulator to fall back on for invalid state.
Guess what's missing in the invalid state check...
I think this should do it:
Until when will it run on an emulator in this case? Will it be too slow
without a slightest hint to the user?
KVM would emulate until the invalid state went away, i.e. until the offending
register was loaded with a new segment that set the Accessed bit.
Such condition will happen
pretty quickly if the emulator
sets the accessed bit also in LDT.
Does it do that?
