From: Corey Minyard <minyard@acm.org>
To: Marc Zyngier <maz@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Corey Minyard <cminyard@mvista.com>
Subject: Re: [PATCH v2] arm64:kgdb: Fix kernel single-stepping
Date: Thu, 20 Feb 2020 08:50:48 -0600 [thread overview]
Message-ID: <20200220145048.GH3704@minyard.net> (raw)
In-Reply-To: <1416dca51b52dff349923184f41d48e8@kernel.org>
On Thu, Feb 20, 2020 at 02:21:36PM +0000, Marc Zyngier wrote:
> On 2020-02-19 15:24, minyard@acm.org wrote:
> > From: Corey Minyard <cminyard@mvista.com>
>
> [...]
>
> > After studying the EL0 handling for this, I realized an issue with using
> > MDSCR to check if single step is enabled: it can be expensive on a VM.
> > So check the task flag first to see if single step is enabled. Then
> > check MDSCR if the task flag is set.
>
> Very tangential remark: I'd really like people *not* to try and optimize
> Linux based on the behaviour of a hypervisor. In general, reading a
> system register is fast, and the fact that it traps on a given hypervisor
> at some point may not be true in the future, nor be a valid assumption
> across hypervisors.
Normally I would agree, but I based this upon git commit
https://github.com/torvalds/linux/commit/2a2830703a2371b47f7b50b1d35cb15dc0e2b717
which seemed to say that it was a significant enough factor to do in the
EL0 case.
-corey
>
> M.
> --
> Jazz is not dead. It just smells funny...
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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
WARNING: multiple messages have this Message-ID (diff)
From: Corey Minyard <minyard@acm.org>
To: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-arm-kernel@lists.infradead.org,
Corey Minyard <cminyard@mvista.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] arm64:kgdb: Fix kernel single-stepping
Date: Thu, 20 Feb 2020 08:50:48 -0600 [thread overview]
Message-ID: <20200220145048.GH3704@minyard.net> (raw)
In-Reply-To: <1416dca51b52dff349923184f41d48e8@kernel.org>
On Thu, Feb 20, 2020 at 02:21:36PM +0000, Marc Zyngier wrote:
> On 2020-02-19 15:24, minyard@acm.org wrote:
> > From: Corey Minyard <cminyard@mvista.com>
>
> [...]
>
> > After studying the EL0 handling for this, I realized an issue with using
> > MDSCR to check if single step is enabled: it can be expensive on a VM.
> > So check the task flag first to see if single step is enabled. Then
> > check MDSCR if the task flag is set.
>
> Very tangential remark: I'd really like people *not* to try and optimize
> Linux based on the behaviour of a hypervisor. In general, reading a
> system register is fast, and the fact that it traps on a given hypervisor
> at some point may not be true in the future, nor be a valid assumption
> across hypervisors.
Normally I would agree, but I based this upon git commit
https://github.com/torvalds/linux/commit/2a2830703a2371b47f7b50b1d35cb15dc0e2b717
which seemed to say that it was a significant enough factor to do in the
EL0 case.
-corey
>
> M.
> --
> Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2020-02-20 14:50 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-19 15:24 [PATCH v2] arm64:kgdb: Fix kernel single-stepping minyard
2020-02-19 15:24 ` minyard
2020-02-20 14:06 ` Daniel Thompson
2020-02-20 14:06 ` Daniel Thompson
2020-02-20 14:52 ` Corey Minyard
2020-02-20 14:52 ` Corey Minyard
2020-02-20 14:21 ` Marc Zyngier
2020-02-20 14:21 ` Marc Zyngier
2020-02-20 14:50 ` Corey Minyard [this message]
2020-02-20 14:50 ` Corey Minyard
2020-02-20 15:06 ` Marc Zyngier
2020-02-20 15:06 ` Marc Zyngier
2020-02-20 14:22 ` Will Deacon
2020-02-20 14:22 ` Will Deacon
2020-02-20 16:30 ` Corey Minyard
2020-02-20 16:30 ` Corey Minyard
2020-02-20 21:30 ` Corey Minyard
2020-02-20 21:30 ` Corey Minyard
2020-02-24 18:07 ` James Morse
2020-02-24 18:07 ` James Morse
2020-02-25 15:38 ` Corey Minyard
2020-02-25 15:38 ` Corey Minyard
2020-02-25 17:55 ` James Morse
2020-02-25 17:55 ` James Morse
2020-02-26 2:58 ` Corey Minyard
2020-02-26 2:58 ` Corey Minyard
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