From: Paolo Bonzini <pbonzini@redhat.com>
To: Kyle Huey <me@kylehuey.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, "Joerg Roedel" <joro@8bytes.org>,
"kvm list" <kvm@vger.kernel.org>,
"open list" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 5/5] KVM: VMX: Handle RFLAGS.TF in skip_emulated_instruction
Date: Mon, 28 Nov 2016 23:43:02 +0100 [thread overview]
Message-ID: <e9b65e89-ad5e-9e7e-4721-4e24c6681891@redhat.com> (raw)
In-Reply-To: <CAP045ArknpKMBts1m0geo7iMsxib-7kCp-8=JvR93g6WvXJz7w@mail.gmail.com>
On 28/11/2016 19:34, Kyle Huey wrote:
>> > The Intel manual says "The processor clears the TF flag before calling
>> > the exception handler" (17.3.1.4), so I think you should do it too.
> The processor does this automatically. "When accessing an exception or
> interrupt handler through either an interrupt gate or a trap gate, the
> processor clears the TF flag in the EFLAGS register after it saves the
> contents of the EFLAGS register on the stack." (Vol 3, 6.12.1.2)
> Empirically, this holds when injecting an exception on VM entry. If
> you take the x86/debug.c test from kvm-unit-tests and inspect RFLAGS
> in handle_db (not regs->rflags, but the actual RFLAGS register while
> running the exception handler) the TF is clear. And, if you modify my
> patch to clear TF before returning, the single stepping ceases after
> the CPUID instruction because the TF was in fact cleared for good.
Ok, then that would be a bug in kvm_vcpu_check_singlestep (because
kvm_vcpu_check_singlestep is mostly interesting for real mode emulation,
I checked kvm_inject_realmode_interrupt and it clears TF too, in
__emulate_int_real).
Paolo
prev parent reply other threads:[~2016-11-28 22:43 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-28 4:18 [PATCH 0/5] KVM: VMX: Fix single stepping with emulated instructions Kyle Huey
2016-11-28 4:18 ` [PATCH 1/5] KVM: x86: Add a return value to kvm_emulate_cpuid Kyle Huey
2016-11-28 4:18 ` [PATCH 2/5] KVM: VMX: Reorder some skip_emulated_instruction calls Kyle Huey
2016-11-28 4:18 ` [PATCH 3/5] KVM: VMX: Move skip_emulated_instruction out of nested_vmx_check_vmcs12 Kyle Huey
2016-11-28 4:18 ` [PATCH 4/5] KVM: x86: Add a return value to skip_emulated_instruction and propagate it Kyle Huey
2016-11-28 4:18 ` [PATCH 5/5] KVM: VMX: Handle RFLAGS.TF in skip_emulated_instruction Kyle Huey
2016-11-28 11:42 ` Paolo Bonzini
2016-11-28 16:13 ` Kyle Huey
2016-11-28 17:19 ` Paolo Bonzini
2016-11-28 18:34 ` Kyle Huey
2016-11-28 22:43 ` Paolo Bonzini [this message]
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