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From: Marc Zyngier <marc.zyngier@arm.com>
To: Peter Maydell <peter.maydell@linaro.org>,
	Christoffer Dall <christoffer.dall@linaro.org>
Cc: arm-mail-list <linux-arm-kernel@lists.infradead.org>,
	Shannon Zhao <shannon.zhao@linaro.org>,
	kvm-devel <kvm@vger.kernel.org>,
	"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>
Subject: Re: [PATCH 1/2] arm: KVM: Do not update PC if the trap handler has updated it
Date: Thu, 07 Jan 2016 08:50:21 +0000	[thread overview]
Message-ID: <568E26CD.8020500@arm.com> (raw)
In-Reply-To: <CAFEAcA9dALQv8Xcyg5FLAvRaJfH5UT2u4jrLjofLh5Ff2yo=8Q@mail.gmail.com>

On 22/12/15 14:50, Peter Maydell wrote:
> On 22 December 2015 at 14:39, Christoffer Dall
> <christoffer.dall@linaro.org> wrote:
>> On Tue, Dec 22, 2015 at 11:08:10AM +0000, Peter Maydell wrote:
>>> Won't this result in our incorrectly skipping the first insn
>>> in the fault handler if the original offending instruction
>>> was itself the first insn in the fault handler?
>>>
>> Wouldn't that then loop with the exception forever?
> 
> Yes, but so would real hardware...

Indeed. As it is, this patch is not doing what it should. On the other
hand, I came to the conclusion that we do not need to fix this just yet,
as long as we only let KVM inject an UNDEF, and that's what the PMU code
requires.

I'll comment on the PMU thread, but the gist of it is:
1) fix the arm64 UNDEF/PABRT/DABRT code to properly account for the the
source EL (Table D1-7 of the ARMv8 ARM).
2) instead of crafting an exception that modifies the PC, fail the
sysreg access and let KVM inject an UNDEF.

I'll post another patch today to address 1), and I'll finish reviewing
the PMU thread (I have a separate patch addressing 2)).

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

WARNING: multiple messages have this Message-ID (diff)
From: marc.zyngier@arm.com (Marc Zyngier)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 1/2] arm: KVM: Do not update PC if the trap handler has updated it
Date: Thu, 07 Jan 2016 08:50:21 +0000	[thread overview]
Message-ID: <568E26CD.8020500@arm.com> (raw)
In-Reply-To: <CAFEAcA9dALQv8Xcyg5FLAvRaJfH5UT2u4jrLjofLh5Ff2yo=8Q@mail.gmail.com>

On 22/12/15 14:50, Peter Maydell wrote:
> On 22 December 2015 at 14:39, Christoffer Dall
> <christoffer.dall@linaro.org> wrote:
>> On Tue, Dec 22, 2015 at 11:08:10AM +0000, Peter Maydell wrote:
>>> Won't this result in our incorrectly skipping the first insn
>>> in the fault handler if the original offending instruction
>>> was itself the first insn in the fault handler?
>>>
>> Wouldn't that then loop with the exception forever?
> 
> Yes, but so would real hardware...

Indeed. As it is, this patch is not doing what it should. On the other
hand, I came to the conclusion that we do not need to fix this just yet,
as long as we only let KVM inject an UNDEF, and that's what the PMU code
requires.

I'll comment on the PMU thread, but the gist of it is:
1) fix the arm64 UNDEF/PABRT/DABRT code to properly account for the the
source EL (Table D1-7 of the ARMv8 ARM).
2) instead of crafting an exception that modifies the PC, fail the
sysreg access and let KVM inject an UNDEF.

I'll post another patch today to address 1), and I'll finish reviewing
the PMU thread (I have a separate patch addressing 2)).

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

  reply	other threads:[~2016-01-07  8:50 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-12-22  9:55 [PATCH 0/2] Fix PC corruption when injecting a fault Marc Zyngier
2015-12-22  9:55 ` Marc Zyngier
2015-12-22  9:55 ` [PATCH 1/2] arm: KVM: Do not update PC if the trap handler has updated it Marc Zyngier
2015-12-22  9:55   ` Marc Zyngier
2015-12-22 10:35   ` Shannon Zhao
2015-12-22 10:35     ` Shannon Zhao
2015-12-22 11:08   ` Peter Maydell
2015-12-22 11:08     ` Peter Maydell
2015-12-22 14:39     ` Christoffer Dall
2015-12-22 14:39       ` Christoffer Dall
2015-12-22 14:50       ` Peter Maydell
2015-12-22 14:50         ` Peter Maydell
2016-01-07  8:50         ` Marc Zyngier [this message]
2016-01-07  8:50           ` Marc Zyngier
2016-01-07  8:59           ` Shannon Zhao
2016-01-07  8:59             ` Shannon Zhao
2016-01-07  9:05             ` Marc Zyngier
2016-01-07  9:05               ` Marc Zyngier
2015-12-22  9:55 ` [PATCH 2/2] arm64: " Marc Zyngier
2015-12-22  9:55   ` Marc Zyngier
2015-12-22 10:15   ` Shannon Zhao
2015-12-22 10:15     ` Shannon Zhao

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