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From: David Hildenbrand <david@redhat.com>
To: Claudio Imbrenda <imbrenda@linux.ibm.com>, kvm@vger.kernel.org
Cc: cohuck@redhat.com, borntraeger@de.ibm.com, frankja@linux.ibm.com,
	thuth@redhat.com, pasic@linux.ibm.com,
	linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
	Ulrich.Weigand@de.ibm.com
Subject: Re: [PATCH v3 02/14] KVM: s390: pv: avoid stall notifications for some UVCs
Date: Fri, 6 Aug 2021 09:30:04 +0200	[thread overview]
Message-ID: <7ef282bb-d90f-9cbb-678b-4293790fb8c6@redhat.com> (raw)
In-Reply-To: <20210804154046.88552-3-imbrenda@linux.ibm.com>

On 04.08.21 17:40, 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.

I suggest splitting this change into a separate patch and adding a bit 
more meat to the description why using the other variant is possible in 
the called context. I was kind of surprise to find that change buried in 
this patch.

Then, you can give both patches a more descriptive patch subject.

> 
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Fixes: 214d9bbcd3a672 ("s390/mm: provide memory management functions for protected KVM guests")
> ---
>   arch/s390/kernel/uv.c | 29 +++++++++++++++++++++++------
>   arch/s390/kvm/pv.c    |  2 +-
>   2 files changed, 24 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index aeb0a15bcbb7..68a8fbafcb9c 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -180,7 +180,7 @@ static int make_secure_pte(pte_t *ptep, unsigned long addr,
>   {
>   	pte_t entry = READ_ONCE(*ptep);
>   	struct page *page;
> -	int expected, rc = 0;
> +	int expected, cc = 0;
>   
>   	if (!pte_present(entry))
>   		return -ENXIO;
> @@ -196,12 +196,25 @@ 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);
> +	/*
> +	 * If the UVC does not succeed or fail immediately, we don't want to
> +	 * loop for long, or we might get stall notifications.
> +	 * On the other hand, this is a complex scenario and we are holding a lot of
> +	 * locks, so we can't easily sleep and reschedule. We try only once,
> +	 * and if the UVC returned busy or partial completion, we return
> +	 * -EAGAIN and we let the callers deal with it.
> +	 */
> +	cc = __uv_call(0, (u64)uvcb);
>   	page_ref_unfreeze(page, expected);
> -	/* Return -ENXIO if the page was not mapped, -EINVAL otherwise */
> -	if (rc)
> -		rc = uvcb->rc == 0x10a ? -ENXIO : -EINVAL;
> -	return rc;
> +	/*
> +	 * Return -ENXIO if the page was not mapped, -EINVAL for other errors.
> +	 * If busy or partially completed, return -EAGAIN.
> +	 */
> +	if (cc == UVC_CC_OK)
> +		return 0;
> +	else if (cc == UVC_CC_BUSY || cc == UVC_CC_PARTIAL)
> +		return -EAGAIN;
> +	return uvcb->rc == 0x10a ? -ENXIO : -EINVAL;
>   }

That looks conceptually like the right thing to me.

-- 
Thanks,

David / dhildenb


  reply	other threads:[~2021-08-06  7:30 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-04 15:40 [PATCH v3 00/14] KVM: s390: pv: implement lazy destroy Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 01/14] KVM: s390: pv: add macros for UVC CC values Claudio Imbrenda
2021-08-06  7:26   ` David Hildenbrand
2021-08-06  9:34     ` Claudio Imbrenda
2021-08-06 15:15     ` Janosch Frank
2021-08-04 15:40 ` [PATCH v3 02/14] KVM: s390: pv: avoid stall notifications for some UVCs Claudio Imbrenda
2021-08-06  7:30   ` David Hildenbrand [this message]
2021-08-06  9:33     ` Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 03/14] KVM: s390: pv: leak the ASCE page when destroy fails Claudio Imbrenda
2021-08-06  7:31   ` David Hildenbrand
2021-08-06  9:32     ` Claudio Imbrenda
2021-08-06 11:39       ` David Hildenbrand
2021-08-04 15:40 ` [PATCH v3 04/14] KVM: s390: pv: properly handle page flags for protected guests Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 05/14] KVM: s390: pv: handle secure storage violations " Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 06/14] KVM: s390: pv: handle secure storage exceptions for normal guests Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 07/14] KVM: s390: pv: refactor s390_reset_acc Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 08/14] KVM: s390: pv: usage counter instead of flag Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 09/14] KVM: s390: pv: add export before import Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 10/14] KVM: s390: pv: lazy destroy for reboot Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 11/14] KVM: s390: pv: extend lazy destroy to handle shutdown Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 12/14] KVM: s390: pv: module parameter to fence lazy destroy Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 13/14] KVM: s390: pv: add OOM notifier for " Claudio Imbrenda
2021-08-04 15:40 ` [PATCH v3 14/14] KVM: s390: pv: avoid export before import if possible Claudio Imbrenda
2021-08-06  7:10 ` [PATCH v3 00/14] KVM: s390: pv: implement lazy destroy David Hildenbrand
2021-08-06  9:30   ` Claudio Imbrenda
2021-08-06 11:30     ` David Hildenbrand
2021-08-06 13:44       ` Claudio Imbrenda
2021-08-09  8:50         ` David Hildenbrand

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