From: Julien Grall <julien@xen.org>
To: Jan Beulich <jbeulich@suse.com>
Cc: "Stefano Stabellini" <sstabellini@kernel.org>,
"Wei Liu" <wl@xen.org>,
"Andrew Cooper" <andrew.cooper3@citrix.com>,
"Julien Grall" <julien.grall@gmail.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
"Volodymyr Babchuk" <volodymyr_babchuk@epam.com>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [PATCH] x86: move vgc_flags to struct pv_vcpu
Date: Fri, 3 Jan 2020 11:48:13 +0000 [thread overview]
Message-ID: <022e3f4e-3b59-5648-1147-eed045b90f81@xen.org> (raw)
In-Reply-To: <96678d3a-1b2f-9ff5-6b92-1ce1ae51e23b@suse.com>
Hi Jan,
Thank you for the information.
On 03/01/2020 11:31, Jan Beulich wrote:
> On 03.01.2020 12:19, Julien Grall wrote:
>> How do you manage secondary CPUs on HVM/PVH guest?
>
> Secondary CPUs have architectural state they start with, and
> there's very little control an OS has over initial register
> state: There's just an 8-bit value specifying (part of) the
> address the CPU should start executing from. All other
> registers get set to hard coded values. And that 8-bit value
> is part of the IPI message the primary CPU sends to the AP
> to be brought up (i.e. there's no hypercall involved here).
Do you have any pointer to this code? Can a CPU be turned off afterwards
and then boot again?
>
> For PVH, a variant of the normal PV model of starting vCPU-s
> gets used, i.e. via VCPUOP_initialise.
In the case of PSCI, I think it is between the two. We are using a
generic hypercall, yet most of the state is fixed.
But as the guest OS may run a CPU for a while, turning off and then boot
again, we need to be able to set the state again. Hence, the
arch_set_guest_info() is quite convenient to use to reset the CPU state.
Cheers,
--
Julien Grall
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next prev parent reply other threads:[~2020-01-03 11:48 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-20 13:55 [Xen-devel] [PATCH] x86: move vgc_flags to struct pv_vcpu Jan Beulich
2019-12-20 14:39 ` Andrew Cooper
2019-12-23 17:33 ` Julien Grall
2019-12-27 8:17 ` Jan Beulich
2019-12-27 11:27 ` Julien Grall
2019-12-27 12:14 ` Jan Beulich
2020-01-03 10:56 ` Julien Grall
2020-01-03 11:05 ` Jan Beulich
2020-01-03 11:19 ` Julien Grall
2020-01-03 11:31 ` Jan Beulich
2020-01-03 11:48 ` Julien Grall [this message]
2020-01-03 12:11 ` Jan Beulich
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