From: Eric Farman <farman@linux.ibm.com>
To: Christian Borntraeger <borntraeger@linux.ibm.com>,
David Hildenbrand <david@redhat.com>,
Janosch Frank <frankja@linux.ibm.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Sven Schnelle <svens@linux.ibm.com>
Subject: Re: [PATCH] KVM: s390: vsie: retry SIE instruction on host intercepts
Date: Tue, 30 Apr 2024 15:31:07 -0400 [thread overview]
Message-ID: <0cfe41f08d89481125ddc1f0087af6bd6bcd1b39.camel@linux.ibm.com> (raw)
In-Reply-To: <dceeac23-0c58-4c78-850a-d09e7b45d6e8@linux.ibm.com>
On Mon, 2024-04-29 at 12:18 +0200, Christian Borntraeger wrote:
> Am 04.03.24 um 16:37 schrieb Eric Farman:
> > On Mon, 2024-03-04 at 09:44 +0100, Christian Borntraeger wrote:
> > >
> > >
> > > Am 04.03.24 um 09:35 schrieb David Hildenbrand:
> > > > On 01.03.24 21:43, Eric Farman wrote:
> > > > > It's possible that SIE exits for work that the host needs to
> > > > > perform
> > > > > rather than something that is intended for the guest.
> > > > >
> > > > > A Linux guest will ignore this intercept code since there is
> > > > > nothing
> > > > > for it to do, but a more robust solution would rewind the PSW
> > > > > back to
> > > > > the SIE instruction. This will transparently resume the guest
> > > > > once
> > > > > the host completes its work, without the guest needing to
> > > > > process
> > > > > what is effectively a NOP and re-issue SIE itself.
> > > >
> > > > I recall that 0-intercepts are valid by the architecture.
> > > > Further,
> > > > I recall that there were some rather tricky corner cases where
> > > > avoiding 0-intercepts would not be that easy.
> >
> > Any chance you recall any details of those corner cases? I can try
> > to
> > chase some of them down.
> >
> > > >
> > > > Now, it's been a while ago, and maybe I misremember. SoI'm
> > > > trusting
> > > > people with access to documentation can review this.
> > >
> > > Yes, 0-intercepts are allowed, and this also happens when LPAR
> > > has an
> > > exit.
> >
> > From an offline conversation I'd had some months back:
> >
> > """
> > The arch does allow ICODE=0 to be stored, but it's supposed to
> > happen
> > only upon a host interruption -- in which case the old PSW is
> > supposed
> > to point back at the SIE, to resume guest execution if the host
> > should
> > LPSW oldPSW.
> > """
>
> Just re-read the architecture again and I agree, the SIE instruction
> should
> be nullified. So we should go forward with this somehow.
>
> Eric, can you maybe add this to devel for CI coverage so that we see
> if there
> are corner cases?
Sure thing.
> Maybe also try to do some performance things (how many IPIs
> can we get in guest2 when a guest3 is running and how many IPIs are
> possible
> in a guest3).
>
Fair enough. I'll see if I can come up with something and report back
here.
prev parent reply other threads:[~2024-04-30 19:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-01 20:43 [PATCH] KVM: s390: vsie: retry SIE instruction on host intercepts Eric Farman
2024-03-04 8:35 ` David Hildenbrand
2024-03-04 8:44 ` Christian Borntraeger
2024-03-04 15:37 ` Eric Farman
2024-04-29 10:18 ` Christian Borntraeger
2024-04-30 19:31 ` Eric Farman [this message]
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=0cfe41f08d89481125ddc1f0087af6bd6bcd1b39.camel@linux.ibm.com \
--to=farman@linux.ibm.com \
--cc=agordeev@linux.ibm.com \
--cc=borntraeger@linux.ibm.com \
--cc=david@redhat.com \
--cc=frankja@linux.ibm.com \
--cc=gor@linux.ibm.com \
--cc=hca@linux.ibm.com \
--cc=imbrenda@linux.ibm.com \
--cc=kvm@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=svens@linux.ibm.com \
/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 read-only IMAP folder(s) and NNTP newsgroup(s).