From: Sean Christopherson <seanjc@google.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Maxim Levitsky <mlevitsk@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, Kieran Bingham <kbingham@kernel.org>,
Jan Kiszka <jan.kiszka@siemens.com>,
Andrew Jones <drjones@redhat.com>,
Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, Johannes Berg <johannes.berg@intel.com>,
Wanpeng Li <wanpengli@tencent.com>,
"H. Peter Anvin" <hpa@zytor.com>, Jessica Yu <jeyu@kernel.org>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Yang Weijiang <weijiang.yang@intel.com>,
linux-kernel@vger.kernel.org, Borislav Petkov <bp@alien8.de>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
Shuah Khan <shuah@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v3 6/6] KVM: selftests: test KVM_GUESTDBG_BLOCKIRQ
Date: Tue, 2 Nov 2021 18:45:19 +0000 [thread overview]
Message-ID: <YYGHPyhFRHHQsX6a@google.com> (raw)
In-Reply-To: <87fsseo7iu.fsf@vitty.brq.redhat.com>
On Tue, Nov 02, 2021, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@google.com> writes:
> > But that mess is a red herring, the test fails with the same signature with APICv=1
> > if the STI is replaced by PUSHF+BTS+POPFD (to avoid the STI shadow). We all missed
> > this key detail from Vitaly's report:
> >
> > SINGLE_STEP[1]: exit 8 exception 1 rip 0x402a25 (should be 0x402a27) dr6 0xffff4ff0 (should be 0xffff4ff0)
> > ^^^^^^
> >
> > Exit '8' is KVM_EXIT_SHUTDOWN, i.e. the arrival of the IRQ hosed the guest because
> > the test doesn't invoke vm_init_descriptor_tables() to install event handlers.
> > The "exception 1" shows up because the run page isn't sanitized by the test, i.e.
> > it's stale data that happens to match.
> >
> > So I would fully expect this test to fail with AVIC=1. The problem is that
> > KVM_GUESTDBG_BLOCKIRQ does absolutely nothing to handle APICv interrupts. And
> > even if KVM does something to fudge that behavior in the emulated local APIC, the
> > test will then fail miserably virtual IPIs (currently AVIC only).
>
> FWIW, the test doesn't seem to fail on my AMD EPYC system even with "avic=1" ...
Huh. Assuming the IRQ is pending in the vIRR and KVM didn't screw up elsewhere,
that seems like a CPU AVIC bug. #DBs have priority over IRQs, but single-step
#DBs are trap-like and KVM (hopefully) isn't injecting a #DB, so a pending IRQ
should be taken on the current instruction in the guest when executing VMRUN with
guest.EFLAGS.IF=1,TF=1 since there will be a one-instruction delay before the
single-step #DB kicks in.
next prev parent reply other threads:[~2021-11-02 18:45 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-11 12:29 [PATCH v3 0/6] KVM: my debug patch queue Maxim Levitsky
2021-08-11 12:29 ` [PATCH v3 1/6] KVM: SVM: split svm_handle_invalid_exit Maxim Levitsky
2021-08-11 12:29 ` [PATCH v3 2/6] KVM: x86: add force_intercept_exceptions_mask Maxim Levitsky
2021-09-02 16:56 ` Sean Christopherson
2022-02-08 14:34 ` Maxim Levitsky
2022-03-08 23:37 ` Sean Christopherson
2022-03-09 12:31 ` Maxim Levitsky
2022-03-09 14:03 ` Paolo Bonzini
2022-03-09 15:40 ` Sean Christopherson
2021-08-11 12:29 ` [PATCH v3 3/6] KVM: SVM: implement force_intercept_exceptions_mask Maxim Levitsky
2021-08-11 14:26 ` Maxim Levitsky
2021-09-02 17:34 ` Sean Christopherson
2022-02-08 14:35 ` Maxim Levitsky
2021-08-11 12:29 ` [PATCH v3 4/6] scripts/gdb: rework lx-symbols gdb script Maxim Levitsky
2021-08-11 12:29 ` [PATCH v3 5/6] KVM: x86: implement KVM_GUESTDBG_BLOCKIRQ Maxim Levitsky
2021-08-11 12:29 ` [PATCH v3 6/6] KVM: selftests: test KVM_GUESTDBG_BLOCKIRQ Maxim Levitsky
2021-09-06 11:20 ` Paolo Bonzini
2021-09-06 21:03 ` Maxim Levitsky
2021-11-01 15:43 ` Vitaly Kuznetsov
2021-11-01 16:19 ` Maxim Levitsky
2021-11-01 23:21 ` Sean Christopherson
2021-11-02 10:46 ` Vitaly Kuznetsov
2021-11-02 15:53 ` Sean Christopherson
2021-11-02 16:18 ` Vitaly Kuznetsov
2021-11-02 18:45 ` Sean Christopherson [this message]
2021-11-03 9:04 ` Maxim Levitsky
2021-11-03 9:29 ` [PATCH] KVM: x86: inhibit APICv when KVM_GUESTDBG_BLOCKIRQ active Maxim Levitsky
2021-11-03 9:31 ` Maxim Levitsky
2021-08-11 13:10 ` [PATCH v3 0/6] KVM: my debug patch queue Paolo Bonzini
2021-08-11 13:22 ` Maxim Levitsky
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