From: Oliver Upton <oliver.upton@linux.dev>
To: Sean Christopherson <seanjc@google.com>
Cc: Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org,
Reiji Watanabe <reijiw@google.com>
Subject: Re: [PATCH 2/2] KVM: arm64: selftests: Disable single-step without relying on ucall()
Date: Thu, 17 Nov 2022 00:53:05 +0000 [thread overview]
Message-ID: <Y3WF8YlvFm8NGYHd@google.com> (raw)
In-Reply-To: <20221117002350.2178351-3-seanjc@google.com>
On Thu, Nov 17, 2022 at 12:23:50AM +0000, Sean Christopherson wrote:
> Automatically disable single-step when the guest reaches the end of the
> verified section instead of using an explicit ucall() to ask userspace to
> disable single-step. An upcoming change to implement a pool-based scheme
> for ucall() will add an atomic operation (bit test and set) in the guest
> ucall code, and if the compiler generate "old school" atomics, e.g.
Off topic, but I didn't ask when we were discussing this issue. What is
the atomic used for in the pool-based ucall implementation?
> 40e57c: c85f7c20 ldxr x0, [x1]
> 40e580: aa100011 orr x17, x0, x16
> 40e584: c80ffc31 stlxr w15, x17, [x1]
> 40e588: 35ffffaf cbnz w15, 40e57c <__aarch64_ldset8_sync+0x1c>
>
> the guest will hang as the local exclusive monitor is reset by eret,
> i.e. the stlxr will always fail due to the VM-Exit for the debug
> exception.
... due to the debug exception taken to EL2.
What's a VM-Exit anyways? ;-)
> Link: https://lore.kernel.org/all/20221006003409.649993-8-seanjc@google.com
> Cc: Oliver Upton <oliver.upton@linux.dev>
> Cc: Marc Zyngier <maz@kernel.org>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
With the commit message nit:
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
--
Thanks,
Oliver
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next prev parent reply other threads:[~2022-11-17 0:54 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-17 0:23 [PATCH 0/2] KVM: arm64: selftests: Fixes for single-step test Sean Christopherson
2022-11-17 0:23 ` [PATCH 1/2] KVM: arm64: selftests: Disable single-step with correct KVM define Sean Christopherson
2022-11-17 0:43 ` Oliver Upton
2022-11-17 3:07 ` Reiji Watanabe
2022-11-17 0:23 ` [PATCH 2/2] KVM: arm64: selftests: Disable single-step without relying on ucall() Sean Christopherson
2022-11-17 0:53 ` Oliver Upton [this message]
2022-11-17 1:20 ` Sean Christopherson
2022-11-17 15:19 ` Sean Christopherson
2022-11-17 22:32 ` Sean Christopherson
2022-11-17 7:07 ` Reiji Watanabe
2022-11-17 13:52 ` [PATCH 0/2] KVM: arm64: selftests: Fixes for single-step test Marc Zyngier
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