From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.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, 7 Sep 2018 10:57:22 +0100 [thread overview]
Message-ID: <0f24ce6a-ff4a-002c-db82-890bdd401755@citrix.com> (raw)
In-Reply-To: <5B923B4002000078001E6383@prv1-mh.provo.novell.com>
On 07/09/18 09:48, Jan Beulich wrote:
>>>> 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.
> 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.
There was nothing deliberate here. TBH, I thought the patch had been
pending on the list for longer than it had. Either way, as we are
starting the conversation again...
> The interlock didn't work as intended, I agree, but "serves no purpose"
> is wrong imo.
At the moment, I stand my by statement, because as far as I can tell,
the interlock literally does nothing.
> 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.
What race? What have I overlooked?
~Andrew
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next prev parent reply other threads:[~2018-09-07 9:57 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
2018-09-07 9:57 ` Andrew Cooper [this message]
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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