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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id p17sm17848989wmk.30.2020.01.14.01.30.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Jan 2020 01:30:32 -0800 (PST) From: Vitaly Kuznetsov To: lantianyu1986@gmail.com Cc: linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, sashal@kernel.org, akpm@linux-foundation.org, michael.h.kelley@microsoft.com, decui@microsoft.com Subject: Re: [PATCH] x86/Hyper-V: Balloon up according to request page number In-Reply-To: <20200114074435.12732-1-Tianyu.Lan@microsoft.com> References: <20200114074435.12732-1-Tianyu.Lan@microsoft.com> Date: Tue, 14 Jan 2020 10:30:32 +0100 Message-ID: <87blr6pepz.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org lantianyu1986@gmail.com writes: > From: Tianyu Lan > > Current code has assumption that balloon request memory size aligns > with 2MB. But actually Hyper-V doesn't guarantee such alignment. When > balloon driver receives non-aligned balloon request, it produces warning > and balloon up more memory than requested in order to keep 2MB alignment. > Remove the warning and balloon up memory according to actual requested > memory size. > > Fixes: f6712238471a ("hv: hv_balloon: avoid memory leak on alloc_error of 2MB memory block") > Cc: stable@vger.kernel.org > Signed-off-by: Tianyu Lan > --- > drivers/hv/hv_balloon.c | 7 ++----- > 1 file changed, 2 insertions(+), 5 deletions(-) > > diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c > index 7f3e7ab22d5d..38ad0e44e927 100644 > --- a/drivers/hv/hv_balloon.c > +++ b/drivers/hv/hv_balloon.c > @@ -1684,7 +1684,7 @@ static unsigned int alloc_balloon_pages(struct hv_dynmem_device *dm, > if (num_pages < alloc_unit) > return 0; > > - for (i = 0; (i * alloc_unit) < num_pages; i++) { > + for (i = 0; i < num_pages / alloc_unit; i++) { > if (bl_resp->hdr.size + sizeof(union dm_mem_page_range) > > HV_HYP_PAGE_SIZE) > return i * alloc_unit; > @@ -1722,7 +1722,7 @@ static unsigned int alloc_balloon_pages(struct hv_dynmem_device *dm, > > } > > - return num_pages; > + return i * alloc_unit; > } > > static void balloon_up(union dm_msg_info *msg_info) > @@ -1737,9 +1737,6 @@ static void balloon_up(union dm_msg_info *msg_info) > long avail_pages; > unsigned long floor; > > - /* The host balloons pages in 2M granularity. */ > - WARN_ON_ONCE(num_pages % PAGES_IN_2M != 0); > - > /* > * We will attempt 2M allocations. However, if we fail to > * allocate 2M chunks, we will go back to PAGE_SIZE allocations. This looks correct but I've noticed we also have /* Refuse to balloon below the floor, keep the 2M granularity. */ if (avail_pages < num_pages || avail_pages - num_pages < floor) { pr_warn("Balloon request will be partially fulfilled. %s\n", avail_pages < num_pages ? "Not enough memory." : "Balloon floor reached."); num_pages = avail_pages > floor ? (avail_pages - floor) : 0; num_pages -= num_pages % PAGES_IN_2M; } in balloon_up(). If 2M granularity is not guaranteed in the first place we can't keep it. Also, when alloc_balloon_pages() is called with 2M alloc_unit and the region is not 2M aligned, it will return someething < num_pages, the next condition, however, only checks for 0: if (alloc_unit != 1 && num_ballooned == 0) { alloc_unit = 1; continue; } we will proceed to sending a response to server and try doing next iteration by calling alloc_balloon_pages() with 2M alloc_unit again, this will finally return 0 and we will switch to 4k. I think we can optimize this to: if (alloc_unit != 1 && num_ballooned != num_pages) { alloc_unit = 1; continue; } -- Vitaly