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From: Claudio Imbrenda <imbrenda@linux.ibm.com>
To: Cornelia Huck <cohuck@redhat.com>
Cc: kvm@vger.kernel.org, borntraeger@de.ibm.com,
	frankja@linux.ibm.com, thuth@redhat.com, pasic@linux.ibm.com,
	david@redhat.com, linux-s390@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 01/13] KVM: s390: pv: avoid stall notifications for some UVCs
Date: Thu, 29 Jul 2021 15:22:05 +0200	[thread overview]
Message-ID: <20210729152205.73d39a65@p-imbrenda> (raw)
In-Reply-To: <87h7gd2y5c.fsf@redhat.com>

On Thu, 29 Jul 2021 12:49:03 +0200
Cornelia Huck <cohuck@redhat.com> wrote:

> On Wed, Jul 28 2021, Claudio Imbrenda <imbrenda@linux.ibm.com> wrote:
> 
> > Improve make_secure_pte to avoid stalls when the system is heavily
> > overcommitted. This was especially problematic in
> > kvm_s390_pv_unpack, because of the loop over all pages that needed
> > unpacking.
> >
> > Also fix kvm_s390_pv_init_vm to avoid stalls when the system is
> > heavily overcommitted.
> >
> > Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> > ---
> >  arch/s390/kernel/uv.c | 11 ++++++++---
> >  arch/s390/kvm/pv.c    |  2 +-
> >  2 files changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> > index aeb0a15bcbb7..fd0faa51c1bb 100644
> > --- a/arch/s390/kernel/uv.c
> > +++ b/arch/s390/kernel/uv.c
> > @@ -196,11 +196,16 @@ static int make_secure_pte(pte_t *ptep,
> > unsigned long addr, if (!page_ref_freeze(page, expected))
> >  		return -EBUSY;
> >  	set_bit(PG_arch_1, &page->flags);
> > -	rc = uv_call(0, (u64)uvcb);
> > +	rc = __uv_call(0, (u64)uvcb);
> >  	page_ref_unfreeze(page, expected);
> > -	/* Return -ENXIO if the page was not mapped, -EINVAL
> > otherwise */
> > -	if (rc)
> > +	/*
> > +	 * Return -ENXIO if the page was not mapped, -EINVAL for
> > other errors.
> > +	 * If busy or partially completed, return -EAGAIN.
> > +	 */
> > +	if (rc == 1)
> >  		rc = uvcb->rc == 0x10a ? -ENXIO : -EINVAL;
> > +	else if (rc > 1)
> > +		rc = -EAGAIN;
> >  	return rc;
> >  }  
> 
> Possibly dumb question: when does the call return > 1?

this is exactly what Janosch meant :)

the next version will have #defines for the 4 possible CC values.

in short:
0 OK
1 error
2 busy (nothing done, try again)
3 partial (something done but not all, try again)

> gmap_make_secure() will do a wait_on_page_writeback() for -EAGAIN, is
> that always the right thing to do?

it's the easiest way to get to a place where we will be able to
reschedule if needed.

wait_on_page_writeback will probably do nothing in that case because
the page is not in writeback.

(a few minutes later)

actually I have checked, it seems that the -EAGAIN gets eventually
propagated to places where it's not checked properly!

this will need some more fixing


  reply	other threads:[~2021-07-29 13:29 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-28 14:26 [PATCH v2 00/13] KVM: s390: pv: implement lazy destroy Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 01/13] KVM: s390: pv: avoid stall notifications for some UVCs Claudio Imbrenda
2021-07-29  9:58   ` Janosch Frank
2021-07-29 12:52     ` Claudio Imbrenda
2021-07-29 10:49   ` Cornelia Huck
2021-07-29 13:22     ` Claudio Imbrenda [this message]
2021-07-28 14:26 ` [PATCH v2 02/13] KVM: s390: pv: leak the ASCE page when destroy fails Claudio Imbrenda
2021-07-29 10:41   ` Janosch Frank
2021-07-29 12:54     ` Claudio Imbrenda
2021-07-29 13:45       ` Janosch Frank
2021-07-28 14:26 ` [PATCH v2 03/13] KVM: s390: pv: properly handle page flags for protected guests Claudio Imbrenda
2021-07-29 11:43   ` Janosch Frank
2021-07-28 14:26 ` [PATCH v2 04/13] KVM: s390: pv: handle secure storage violations " Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 05/13] KVM: s390: pv: handle secure storage exceptions for normal guests Claudio Imbrenda
2021-07-29 12:17   ` Janosch Frank
2021-07-29 13:28     ` Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 06/13] KVM: s390: pv: refactor s390_reset_acc Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 07/13] KVM: s390: pv: usage counter instead of flag Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 08/13] KVM: s390: pv: add export before import Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 09/13] KVM: s390: pv: lazy destroy for reboot Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 10/13] KVM: s390: pv: extend lazy destroy to handle shutdown Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 11/13] KVM: s390: pv: module parameter to fence lazy destroy Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 12/13] KVM: s390: pv: add OOM notifier for " Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 13/13] KVM: s390: pv: add support for UV feature bits Claudio Imbrenda
2021-07-29  9:52   ` Janosch Frank
2021-07-29 13:28     ` Claudio Imbrenda

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