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From: Andrew Jones <drjones@redhat.com>
To: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>,
	Shannon Zhao <shannon.zhao@linaro.org>,
	Peter Maydell <peter.maydell@linaro.org>,
	linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
	kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH] arm64: KVM: Fix AArch64 guest userspace exception injection
Date: Tue, 12 Jan 2016 20:13:35 +0100	[thread overview]
Message-ID: <20160112191335.GB5795@hawk.localdomain> (raw)
In-Reply-To: <56954992.7000307@arm.com>

On Tue, Jan 12, 2016 at 06:44:34PM +0000, Marc Zyngier wrote:
> On 12/01/16 18:23, Andrew Jones wrote:
> > Hi Marc,
> > 
> > Please shoot me if the following statement is false.
> 
> I wouldn't do that. Having had the privilege to waste 10 months of my
> life doing a military service, I quickly discovered I didn't like
> weapons nor those who carry them...
> 
> > Without this patch, if a guest that is running in, e.g. PSR_MODE_EL0t,
> > tries to do, e.g. 'smc #0', then KVM will inject an undef exception,
> > which should lead to the guest resuming at VBAR_EL1 + 0x400, but instead
> > it resumes at VBAR_EL1 + 0x200.
> 
> Not quite. SMC is undefined at EL0 (see C6.6.165), so it is not trapped
> to EL2, but to EL1. KVM is not in the loop at all in that case.
> 
> > Now, if you haven't started loading your gun to shoot me yet, then I'm
> > quite confused as to why the unit test[1] I wrote for this works just
> > fine without this patch.
> 
> If you want to exercise that path, you have to access something that
> wouldn't trap to EL1, but that EL2 traps. I don't think we have much
> stuff so far that can be used at EL0 and would be trapped to EL2,
> unfortunately (the PMU code is probably the first thing we'll merge).
>
> In the meantime, this test case is fairly pointless, I'm afraid...

Ah, thanks for the clarification, and the lack of desire to shoot me.
I'll stash this test case for a later day.

drew

WARNING: multiple messages have this Message-ID (diff)
From: drjones@redhat.com (Andrew Jones)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] arm64: KVM: Fix AArch64 guest userspace exception injection
Date: Tue, 12 Jan 2016 20:13:35 +0100	[thread overview]
Message-ID: <20160112191335.GB5795@hawk.localdomain> (raw)
In-Reply-To: <56954992.7000307@arm.com>

On Tue, Jan 12, 2016 at 06:44:34PM +0000, Marc Zyngier wrote:
> On 12/01/16 18:23, Andrew Jones wrote:
> > Hi Marc,
> > 
> > Please shoot me if the following statement is false.
> 
> I wouldn't do that. Having had the privilege to waste 10 months of my
> life doing a military service, I quickly discovered I didn't like
> weapons nor those who carry them...
> 
> > Without this patch, if a guest that is running in, e.g. PSR_MODE_EL0t,
> > tries to do, e.g. 'smc #0', then KVM will inject an undef exception,
> > which should lead to the guest resuming at VBAR_EL1 + 0x400, but instead
> > it resumes at VBAR_EL1 + 0x200.
> 
> Not quite. SMC is undefined at EL0 (see C6.6.165), so it is not trapped
> to EL2, but to EL1. KVM is not in the loop at all in that case.
> 
> > Now, if you haven't started loading your gun to shoot me yet, then I'm
> > quite confused as to why the unit test[1] I wrote for this works just
> > fine without this patch.
> 
> If you want to exercise that path, you have to access something that
> wouldn't trap to EL1, but that EL2 traps. I don't think we have much
> stuff so far that can be used at EL0 and would be trapped to EL2,
> unfortunately (the PMU code is probably the first thing we'll merge).
>
> In the meantime, this test case is fairly pointless, I'm afraid...

Ah, thanks for the clarification, and the lack of desire to shoot me.
I'll stash this test case for a later day.

drew

  reply	other threads:[~2016-01-12 19:13 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-07  9:03 [PATCH] arm64: KVM: Fix AArch64 guest userspace exception injection Marc Zyngier
2016-01-07  9:03 ` Marc Zyngier
2016-01-08  8:36 ` Shannon Zhao
2016-01-08  8:36   ` Shannon Zhao
2016-01-08  8:36   ` Shannon Zhao
2016-01-08  8:56   ` Marc Zyngier
2016-01-08  8:56     ` Marc Zyngier
2016-01-11  1:36     ` Shannon Zhao
2016-01-11  1:36       ` Shannon Zhao
2016-01-11  1:36       ` Shannon Zhao
2016-01-10 19:45 ` Christoffer Dall
2016-01-10 19:45   ` Christoffer Dall
2016-01-11 10:06   ` Marc Zyngier
2016-01-11 10:06     ` Marc Zyngier
2016-01-12 18:23 ` Andrew Jones
2016-01-12 18:23   ` Andrew Jones
2016-01-12 18:44   ` Marc Zyngier
2016-01-12 18:44     ` Marc Zyngier
2016-01-12 19:13     ` Andrew Jones [this message]
2016-01-12 19:13       ` Andrew Jones

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