From: stsp <stsp2@yandex.ru>
To: Sean Christopherson <seanjc@google.com>
Cc: Jim Mattson <jmattson@google.com>, kvm list <kvm@vger.kernel.org>
Subject: Re: guest/host mem out of sync on core2duo?
Date: Sat, 19 Jun 2021 12:18:10 +0300 [thread overview]
Message-ID: <bda4611d-3ac7-de7c-44f4-f6fc5ac309f9@yandex.ru> (raw)
In-Reply-To: <YM1AWuoRm6xh+OVr@google.com>
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?
next prev parent reply other threads:[~2021-06-19 9:18 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-12 22:49 guest/host mem out of sync on core2duo? stsp
2021-06-13 12:36 ` stsp
2021-06-14 17:06 ` Sean Christopherson
2021-06-14 17:32 ` stsp
2021-06-17 14:42 ` Sean Christopherson
2021-06-18 15:59 ` stsp
2021-06-18 21:07 ` Jim Mattson
2021-06-18 21:55 ` stsp
2021-06-18 22:06 ` Jim Mattson
2021-06-18 22:26 ` stsp
2021-06-18 22:32 ` Sean Christopherson
2021-06-19 0:11 ` stsp
2021-06-19 0:54 ` Sean Christopherson
2021-06-19 9:18 ` stsp [this message]
2021-06-21 2:34 ` exception vs SIGALRM race (was: Re: guest/host mem out of sync on core2duo?) stsp
2021-06-21 22:33 ` Jim Mattson
2021-06-21 23:32 ` stsp
2021-06-22 0:27 ` stsp
2021-06-28 21:47 ` Jim Mattson
2021-06-28 21:50 ` stsp
2021-06-28 22:00 ` stsp
2021-06-28 22:27 ` Jim Mattson
2021-07-06 16:28 ` Paolo Bonzini
2021-07-06 22:22 ` stsp
2021-07-06 23:41 ` Paolo Bonzini
2021-06-23 23:38 ` exception vs SIGALRM race (with test-case now!) stsp
2021-06-24 0:11 ` stsp
2021-06-24 0:25 ` stsp
2021-06-24 18:05 ` exception vs SIGALRM race on core2 CPUs (with qemu-based test-case this time!) stsp
2021-06-24 18:07 ` stsp
2021-06-25 23:35 ` exception vs SIGALRM race on core2 CPUs (with fix!) stsp
2021-06-26 0:15 ` Jim Mattson
2021-06-26 0:35 ` stsp
2021-06-26 21:50 ` stsp
2021-06-27 12:13 ` stsp
2021-06-26 14:03 ` exception vs SIGALRM race (another patch) stsp
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