From: David Woodhouse <dwmw2@infradead.org>
To: Paul Durrant <paul@xen.org>,
Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 15/15] KVM: xen: allow vcpu_info content to be 'safely' copied
Date: Wed, 22 Nov 2023 10:39:04 +0000 [thread overview]
Message-ID: <7c7238a9c8b0dc6bc865407ba804a651cdfdb044.camel@infradead.org> (raw)
In-Reply-To: <4a76b7dc9055485d9e2592b395e60221dc349abf.camel@infradead.org>
[-- Attachment #1: Type: text/plain, Size: 3000 bytes --]
On Tue, 2023-11-21 at 22:53 +0000, David Woodhouse wrote:
> On Tue, 2023-11-21 at 18:02 +0000, Paul Durrant wrote:
> > From: Paul Durrant <pdurrant@amazon.com>
> >
> > If the guest sets an explicit vcpu_info GPA then, for any of the first 32
> > vCPUs, the content of the default vcpu_info in the shared_info page must be
> > copied into the new location. Because this copy may race with event
> > delivery (which updates the 'evtchn_pending_sel' field in vcpu_info) there
> > needs to be a way to defer that until the copy is complete.
> > Happily there is already a shadow of 'evtchn_pending_sel' in kvm_vcpu_xen
> > that is used in atomic context if the vcpu_info PFN cache has been
> > invalidated so that the update of vcpu_info can be deferred until the
> > cache can be refreshed (on vCPU thread's the way back into guest context).
> >
> > Also use this shadow if the vcpu_info cache has been *deactivated*, so that
> > the VMM can safely copy the vcpu_info content and then re-activate the
> > cache with the new GPA. To do this, stop considering an inactive vcpu_info
> > cache as a hard error in kvm_xen_set_evtchn_fast().
> >
> > Signed-off-by: Paul Durrant <pdurrant@amazon.com>
> > Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
>
> Wait, didn't we realise that this leaves the bits set in the shadow
> evtchn_pending_sel that get lost on migration?
>
> The point in your previous patch which split out a shiny new
> set_shinfo_evtchn_pending() function was that you could then *call*
> that function to ensure that the corresponding index bit was set on the
> destination host after migration, if the bit in the shinfo is.
>
> So we'd do that from kvm_xen_setup_evtchn(), kvm_xen_eventfd_assign(),
> and when setting KVM_XEN_VCPU_ATTR_TYPE_TIMER.
>
> if (bit_is_set_in_shinfo)
> set_shinfo_evtchn_pending()
I mean set_vcpu_info_evtchn_pending() of course. And we probably want
to extend the xen_shinfo_test to test it, by setting the bit in the
shinfo to mark the event as pending, and then doing each of
• Set up timer (a bit like in TEST_TIMER_RESTORE at line 817).
• Add incoming eventfd with KVM_SET_GSI_ROUTING (cf. line 563)
• Add IPI with KVM_XEN_ATTR_TYPE_EVTCHN (cf. line 597)
Each of those should set the index bit in the vcpu_info immediately if
the evtchn port is already set (and unmasked) in the shinfo.
(Ignore this part if you're cleverer than me or have had more coffee…)
It took me a moment to get my head around the different setups we have
for event channels, but that's because the standard KVM_SET_GSI_ROUTING
one is for *incoming* events, just as we would for MSIs, and we use the
standard way of attaching an eventfd to an incoming GSI/MSI/evtchn.
The KVM_XEN_ATTR_TYPE_EVTCHN one is for *outbound* events where the
guest does an EVTCHNOP_send. That can *raise* events on an eventfd, or
it can be an IPI or loopback interdomain port, which is the case we
need to test.
[-- Attachment #2: smime.p7s --]
[-- Type: application/pkcs7-signature, Size: 5965 bytes --]
next prev parent reply other threads:[~2023-11-22 10:39 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-21 18:02 [PATCH v8 00/15] KVM: xen: update shared_info and vcpu_info handling Paul Durrant
2023-11-21 18:02 ` [PATCH v8 01/15] KVM: pfncache: Add a map helper function Paul Durrant
2023-11-21 18:02 ` [PATCH v8 02/15] KVM: pfncache: remove unnecessary exports Paul Durrant
2023-11-21 21:49 ` David Woodhouse
2023-11-22 8:44 ` Paul Durrant
2023-11-21 18:02 ` [PATCH v8 03/15] KVM: xen: mark guest pages dirty with the pfncache lock held Paul Durrant
2023-11-21 21:49 ` David Woodhouse
2023-11-21 18:02 ` [PATCH v8 04/15] KVM: pfncache: add a mark-dirty helper Paul Durrant
2023-11-21 18:02 ` [PATCH v8 05/15] KVM: pfncache: remove KVM_GUEST_USES_PFN usage Paul Durrant
2023-11-21 22:24 ` David Woodhouse
2023-11-27 23:36 ` Sean Christopherson
2023-11-21 18:02 ` [PATCH v8 06/15] KVM: pfncache: stop open-coding offset_in_page() Paul Durrant
2023-11-21 22:26 ` David Woodhouse
2023-11-21 18:02 ` [PATCH v8 07/15] KVM: pfncache: include page offset in uhva and use it consistently Paul Durrant
2023-11-21 22:35 ` David Woodhouse
2023-11-22 9:29 ` Paul Durrant
2023-11-22 8:54 ` Xu Yilun
2023-11-22 9:12 ` David Woodhouse
2023-11-22 14:27 ` Xu Yilun
2023-11-22 15:42 ` David Woodhouse
2023-11-22 15:52 ` Paul Durrant
2023-11-21 18:02 ` [PATCH v8 08/15] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA Paul Durrant
2023-11-21 22:47 ` David Woodhouse
2023-11-22 10:07 ` Paul Durrant
2023-11-21 18:02 ` [PATCH v8 09/15] KVM: xen: allow shared_info to be mapped by fixed HVA Paul Durrant
2023-11-21 18:02 ` [PATCH v8 10/15] KVM: xen: allow vcpu_info " Paul Durrant
2023-11-21 18:02 ` [PATCH v8 11/15] KVM: selftests / xen: map shared_info using HVA rather than GFN Paul Durrant
2023-11-21 18:02 ` [PATCH v8 12/15] KVM: selftests / xen: re-map vcpu_info using HVA rather than GPA Paul Durrant
2023-11-21 18:02 ` [PATCH v8 13/15] KVM: xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA capability Paul Durrant
2023-11-21 18:02 ` [PATCH v8 14/15] KVM: xen: split up kvm_xen_set_evtchn_fast() Paul Durrant
2023-11-21 22:49 ` David Woodhouse
2023-11-21 18:02 ` [PATCH v8 15/15] KVM: xen: allow vcpu_info content to be 'safely' copied Paul Durrant
2023-11-21 22:53 ` David Woodhouse
2023-11-22 10:39 ` David Woodhouse [this message]
2023-11-22 10:55 ` Paul Durrant
2023-11-22 11:25 ` David Woodhouse
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=7c7238a9c8b0dc6bc865407ba804a651cdfdb044.camel@infradead.org \
--to=dwmw2@infradead.org \
--cc=bp@alien8.de \
--cc=dave.hansen@linux.intel.com \
--cc=hpa@zytor.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=paul@xen.org \
--cc=pbonzini@redhat.com \
--cc=seanjc@google.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).