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[79.176.40.226]) by smtp.gmail.com with ESMTPSA id c137sm3451372qkg.110.2019.09.04.12.28.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Sep 2019 12:28:48 -0700 (PDT) Date: Wed, 4 Sep 2019 15:28:41 -0400 From: "Michael S. Tsirkin" To: Alexander Duyck Cc: nitesh@redhat.com, kvm@vger.kernel.org, david@redhat.com, dave.hansen@intel.com, linux-kernel@vger.kernel.org, willy@infradead.org, mhocko@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, virtio-dev@lists.oasis-open.org, osalvador@suse.de, yang.zhang.wz@gmail.com, pagupta@redhat.com, riel@surriel.com, konrad.wilk@oracle.com, lcapitulino@redhat.com, wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com, dan.j.williams@intel.com, alexander.h.duyck@linux.intel.com Subject: Re: [PATCH v7 5/6] virtio-balloon: Pull page poisoning config out of free page hinting Message-ID: <20190904152244-mutt-send-email-mst@kernel.org> References: <20190904150920.13848.32271.stgit@localhost.localdomain> <20190904151055.13848.27351.stgit@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190904151055.13848.27351.stgit@localhost.localdomain> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 04, 2019 at 08:10:55AM -0700, Alexander Duyck wrote: > From: Alexander Duyck > > Currently the page poisoning setting wasn't being enabled unless free page > hinting was enabled. However we will need the page poisoning tracking logic > as well for unused page reporting. As such pull it out and make it a > separate bit of config in the probe function. > > In addition we can actually wrap the code in a check for NO_SANITY. If we > don't care what is actually in the page we can just default to 0 and leave > it there. > > Signed-off-by: Alexander Duyck > --- > drivers/virtio/virtio_balloon.c | 19 +++++++++++++------ > mm/page_reporting.c | 4 ++++ > 2 files changed, 17 insertions(+), 6 deletions(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 226fbb995fb0..2c19457ab573 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -842,7 +842,6 @@ static int virtio_balloon_register_shrinker(struct virtio_balloon *vb) > static int virtballoon_probe(struct virtio_device *vdev) > { > struct virtio_balloon *vb; > - __u32 poison_val; > int err; > > if (!vdev->config->get) { > @@ -909,11 +908,19 @@ static int virtballoon_probe(struct virtio_device *vdev) > VIRTIO_BALLOON_CMD_ID_STOP); > spin_lock_init(&vb->free_page_list_lock); > INIT_LIST_HEAD(&vb->free_page_list); > - if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) { > - memset(&poison_val, PAGE_POISON, sizeof(poison_val)); > - virtio_cwrite(vb->vdev, struct virtio_balloon_config, > - poison_val, &poison_val); > - } > + } > + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_PAGE_POISON)) { > + __u32 poison_val = 0; > + > +#if !defined(CONFIG_PAGE_POISONING_NO_SANITY) > + /* > + * Let hypervisor know that we are expecting a specific > + * value to be written back in unused pages. > + */ > + memset(&poison_val, PAGE_POISON, sizeof(poison_val)); > +#endif > + virtio_cwrite(vb->vdev, struct virtio_balloon_config, > + poison_val, &poison_val); > } > /* > * We continue to use VIRTIO_BALLOON_F_DEFLATE_ON_OOM to decide if a I'm a bit confused by this part. Should we not just clear VIRTIO_BALLOON_F_PAGE_POISON completely? In my mind the value written should be what guest puts in free pages - and possibly what it expects to find there later. If it doesn't expect anything there then it makes sense to clear VIRTIO_BALLOON_F_PAGE_POISON so that host does not try to put the poison value there. But I think that it does not make sense to lie to host about the poison value - I think that if we do send poison value to host it's reasonable for host to expect free pages have that value - and even possibly to validate that. So I think that the hack belongs in virtballoon_validate, near the page_poisoning_enabled check. > diff --git a/mm/page_reporting.c b/mm/page_reporting.c > index 5006b08d5eec..35c0fe4c4471 100644 > --- a/mm/page_reporting.c > +++ b/mm/page_reporting.c > @@ -299,6 +299,10 @@ int page_reporting_startup(struct page_reporting_dev_info *phdev) > struct zone *zone; > int err = 0; > > + /* No point in enabling this if it cannot handle any pages */ > + if (!phdev->capacity) > + return -EINVAL; > + > mutex_lock(&page_reporting_mutex); > > /* nothing to do if already in use */