linux-kernel - Re: [PATCH v2 01/13] KVM: s390: pv: avoid stall notifications for some UVCs

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Message-ID: <20210729145204.2d8c1430@p-imbrenda>
Date:   Thu, 29 Jul 2021 14:52:04 +0200
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     Janosch Frank <frankja@...ux.ibm.com>
Cc:     kvm@...r.kernel.org, cohuck@...hat.com, borntraeger@...ibm.com,
        thuth@...hat.com, pasic@...ux.ibm.com, david@...hat.com,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 01/13] KVM: s390: pv: avoid stall notifications for
 some UVCs

On Thu, 29 Jul 2021 11:58:39 +0200
Janosch Frank <frankja@...ux.ibm.com> wrote:

> On 7/28/21 4:26 PM, Claudio Imbrenda 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.  
> 
> Fixes tag?

will be in the next version

> > 
> > Signed-off-by: Claudio Imbrenda <imbrenda@...ux.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);  
> 
> We should exchange rc with cc since that's what we get back from
> __uv_call(). Technically we always get a cc but for the other
> functions it's only ever 0/1 which translates to success/error so rc
> is ok.

will be in the next version

> >  	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;  
> 
> Could you define the CCs in uv.h and check against the constants here
> so it's easier to understand that the rc > 1 checks against a "UV was
> busy please re-issue the call again" cc?
>
> Maybe also make it explicit for cc 2 and 3 instead of cc > 1

will be in the next version

> >  }
> >  
> > diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> > index c8841f476e91..e007df11a2fe 100644
> > --- a/arch/s390/kvm/pv.c
> > +++ b/arch/s390/kvm/pv.c
> > @@ -196,7 +196,7 @@ int kvm_s390_pv_init_vm(struct kvm *kvm, u16
> > *rc, u16 *rrc) uvcb.conf_base_stor_origin =
> > (u64)kvm->arch.pv.stor_base; uvcb.conf_virt_stor_origin =
> > (u64)kvm->arch.pv.stor_var; 
> > -	cc = uv_call(0, (u64)&uvcb);
> > +	cc = uv_call_sched(0, (u64)&uvcb);
> >  	*rc = uvcb.header.rc;
> >  	*rrc = uvcb.header.rrc;
> >  	KVM_UV_EVENT(kvm, 3, "PROTVIRT CREATE VM: handle %llx len
> > %llx rc %x rrc %x", 
>