From: "Jan Beulich" <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Wei Liu <wei.liu2@citrix.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Tim Deegan <tim@xen.org>, Xen-devel <xen-devel@lists.xen.org>,
Julien Grall <julien.grall@arm.com>
Subject: Re: [PATCH] xen/domctl: Drop vcpu_alloc_lock
Date: Fri, 07 Sep 2018 02:48:00 -0600 [thread overview]
Message-ID: <5B923B4002000078001E6383@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <1536174925-5500-1-git-send-email-andrew.cooper3@citrix.com>
>>> On 05.09.18 at 21:15, <andrew.cooper3@citrix.com> wrote:
> Since its introduction in c/s 8cbb5278e "x86/AMD: Add support for AMD's OSVW
> feature in guests", the OSVW data has been corrected to be per-domain rather
> than per-vcpu, and is initialised during XEN_DOMCTL_createdomain.
>
> Furthermore, because XENPF_microcode_update uses hypercall continuations to
> move between CPUs, it drops the vcpu_alloc_lock mid update, meaning that it
> didn't provided the interlock guarantee that the OSVW patch was looking for in
> the first place.
>
> This interlock serves no purpose, so take the opportunity to drop it and
> remove a global spinlock from the hypervisor.
The interlock didn't work as intended, I agree, but "serves no purpose"
is wrong imo. Rather than blindly dropping the logic, I'd have expected
for it to be fixed: Despite the movement into XEN_DOMCTL_createdomain
there's still a race between ucode updates and domain creation.
I see you've rushed the patch in (perhaps to avoid objections, given
that you've proposed this removal before, and I didn't really like it),
so I guess we need to take it from there now. I certainly agree that
runtime ucode updates aren't in good shape anyway, but I certainly
don't think making a bad situation worse really helps. In any event -
I would have expected you to give a little more time between patch
submission and patch committing, especially when the subject was
previously controversial, no matter that you've has the formally
necessary ack-s (which, if you had pointed out the previous
controversy, might not have been given that easily/quickly).
FAOD I'm not suggesting to revert the patch at this point in time.
Jan
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next prev parent reply other threads:[~2018-09-07 8:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-05 19:15 [PATCH] xen/domctl: Drop vcpu_alloc_lock Andrew Cooper
2018-09-06 9:50 ` George Dunlap
2018-09-06 10:47 ` Wei Liu
2018-09-07 8:48 ` Jan Beulich [this message]
2018-09-07 9:57 ` Andrew Cooper
2018-09-07 10:21 ` Jan Beulich
2018-09-07 10:59 ` Andrew Cooper
2018-09-07 12:37 ` George Dunlap
2018-09-07 12:44 ` Andrew Cooper
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