From: Jan Beulich <jbeulich@suse.com>
To: Julien Grall <julien@xen.org>,
Stefano Stabellini <sstabellini@kernel.org>,
Bertrand Marquis <bertrand.marquis@arm.com>
Cc: xen-devel@lists.xenproject.org,
osstest service owner <osstest-admin@xenproject.org>
Subject: Re: [xen-unstable bisection] complete test-armhf-armhf-xl-multivcpu
Date: Mon, 12 Apr 2021 10:53:56 +0200 [thread overview]
Message-ID: <b7800c49-8106-e2cc-2fa3-9682305f333f@suse.com> (raw)
In-Reply-To: <E1lVPaB-0007ue-Ho@osstest.test-lab.xenproject.org>
On 11.04.2021 04:12, osstest service owner wrote:
> branch xen-unstable
> xenbranch xen-unstable
> job test-armhf-armhf-xl-multivcpu
> testid guest-start/debian.repeat
>
> Tree: linux git://xenbits.xen.org/linux-pvops.git
> Tree: linuxfirmware git://xenbits.xen.org/osstest/linux-firmware.git
> Tree: qemuu git://xenbits.xen.org/qemu-xen.git
> Tree: xen git://xenbits.xen.org/xen.git
>
> *** Found and reproduced problem changeset ***
>
> Bug is in tree: xen git://xenbits.xen.org/xen.git
> Bug introduced: 9617d5f9c19d1d157629e1e436791509526e0ce5
> Bug not present: 5c3c410bd2ea8d2cc520e8e8f83ad143c9c5cff7
> Last fail repro: http://logs.test-lab.xenproject.org/osstest/logs/160931/
>
>
> commit 9617d5f9c19d1d157629e1e436791509526e0ce5
> Author: Julien Grall <jgrall@amazon.com>
> Date: Sat Feb 20 17:54:13 2021 +0000
>
> xen/arm: mm: flush_page_to_ram() only need to clean to PoC
>
> At the moment, flush_page_to_ram() is both cleaning and invalidate to
> PoC the page.
>
> The goal of flush_page_to_ram() is to prevent corruption when the guest
> has disabled the cache (the cache line may be dirty) and the guest to
> read previous content.
>
> Per this definition, the invalidating the line is not necessary. So
> invalidating the cache is unnecessary. In fact, it may be counter-
> productive as the line may be (speculatively) accessed a bit after.
> So this will incurr an expensive access to the memory.
>
> More generally, we should avoid interferring too much with cache.
> Therefore, flush_page_to_ram() is updated to only clean to PoC the page.
>
> The performance impact of this change will depend on your
> workload/processor.
>
> Signed-off-by: Julien Grall <jgrall@amazon.com>
> Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
> Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Is it possible that other code (guest one in particular considering the
failure pattern, but possibly not limited to that) has developed a
dependency on the prior behavior?
Jan
next prev parent reply other threads:[~2021-04-12 8:54 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-11 2:12 [xen-unstable bisection] complete test-armhf-armhf-xl-multivcpu osstest service owner
2021-04-12 8:53 ` Jan Beulich [this message]
2021-04-13 16:17 ` Julien Grall
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