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Fri, 4 Dec 2020 16:52:47 +0000 (GMT) Received: from ram-ibm-com.ibm.com (unknown [9.80.218.6]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Fri, 4 Dec 2020 16:52:47 +0000 (GMT) Date: Fri, 4 Dec 2020 08:52:44 -0800 From: Ram Pai To: Bharata B Rao Subject: Re: [PATCH] powerpc/book3s_hv_uvmem: Check for failed page migration Message-ID: <20201204165244.GA3390@ram-ibm-com.ibm.com> References: <20201203050812.5234-1-alistair@popple.id.au> <20201204101841.GA621541@in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201204101841.GA621541@in.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.312, 18.0.737 definitions=2020-12-04_05:2020-12-04, 2020-12-04 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 priorityscore=1501 malwarescore=0 bulkscore=0 adultscore=0 spamscore=0 impostorscore=0 mlxscore=0 phishscore=0 mlxlogscore=999 clxscore=1011 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012040088 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Ram Pai Cc: Alistair Popple , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Fri, Dec 04, 2020 at 03:48:41PM +0530, Bharata B Rao wrote: > On Thu, Dec 03, 2020 at 04:08:12PM +1100, Alistair Popple wrote: > > migrate_vma_pages() may still clear MIGRATE_PFN_MIGRATE on pages which > > are not able to be migrated. Drivers may safely copy data prior to > > calling migrate_vma_pages() however a remote mapping must not be > > established until after migrate_vma_pages() has returned as the > > migration could still fail. > > > > UV_PAGE_IN_in both copies and maps the data page, therefore it should > > only be called after checking the results of migrate_vma_pages(). > > > > Signed-off-by: Alistair Popple > > --- > > arch/powerpc/kvm/book3s_hv_uvmem.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c > > index 84e5a2dc8be5..08aa6a90c525 100644 > > --- a/arch/powerpc/kvm/book3s_hv_uvmem.c > > +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c > > @@ -762,7 +762,10 @@ static int kvmppc_svm_page_in(struct vm_area_struct *vma, > > goto out_finalize; > > } > > > > - if (pagein) { > > + *mig.dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED; > > + migrate_vma_pages(&mig); > > + > > + if ((*mig.src & MIGRATE_PFN_MIGRATE) && pagein) { > > pfn = *mig.src >> MIGRATE_PFN_SHIFT; > > spage = migrate_pfn_to_page(*mig.src); > > if (spage) { > > @@ -773,8 +776,6 @@ static int kvmppc_svm_page_in(struct vm_area_struct *vma, > > } > > } > > > > - *mig.dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_LOCKED; > > - migrate_vma_pages(&mig); > > out_finalize: > > migrate_vma_finalize(&mig); > > return ret; This patch certainly looks like the problem, that has been hurting us for a while. Let me run this patch through my SVM tests. Looks very promising. BTW: The code does a similar thing while paging out. It pages out from the UV, and then does the migration. Is there a bug there aswell? RP