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Wed, 18 Aug 2021 13:26:23 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 37E824C058; Wed, 18 Aug 2021 13:26:23 +0000 (GMT) Received: from p-imbrenda.bredband2.com (unknown [9.145.14.177]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 18 Aug 2021 13:26:23 +0000 (GMT) From: Claudio Imbrenda To: kvm@vger.kernel.org Cc: cohuck@redhat.com, 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, Ulrich.Weigand@de.ibm.com Subject: [PATCH v4 04/14] KVM: s390: pv: avoid stalls when making pages secure Date: Wed, 18 Aug 2021 15:26:10 +0200 Message-Id: <20210818132620.46770-5-imbrenda@linux.ibm.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20210818132620.46770-1-imbrenda@linux.ibm.com> References: <20210818132620.46770-1-imbrenda@linux.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: 2M-n8KDoYeZNt5RkwZ3JpA99AMb8JUHy X-Proofpoint-GUID: 6QECtlvLqhtMEpmlA4zj13t0wNQWCiVI X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-08-18_04:2021-08-17,2021-08-18 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=999 clxscore=1015 priorityscore=1501 malwarescore=0 impostorscore=0 mlxscore=0 phishscore=0 spamscore=0 bulkscore=0 lowpriorityscore=0 suspectscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108180082 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Due to the locks being held, it was not possible to simply replace uv_call with uv_call_sched. A more complex approach was needed, in which uv_call is replaced with __uv_call, which does not loop. When the UVC needs to be executed again, -EAGAIN is returned, and the caller (or its caller) will try again. When -EAGAIN is returned, the path is the same as when the page is in writeback (and the writeback check is also performed, which is harmless). Signed-off-by: Claudio Imbrenda Fixes: 214d9bbcd3a672 ("s390/mm: provide memory management functions for protected KVM guests") --- arch/s390/kernel/uv.c | 29 +++++++++++++++++++++++------ 1 file changed, 23 insertions(+), 6 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; } /* @@ -254,6 +267,10 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb) mmap_read_unlock(gmap->mm); if (rc == -EAGAIN) { + /* + * If we are here because the UVC returned busy or partial + * completion, this is just a useless check, but it is safe. + */ wait_on_page_writeback(page); } else if (rc == -EBUSY) { /* -- 2.31.1