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Tue, 16 May 2023 07:30:02 -0700 (PDT) Date: Tue, 16 May 2023 07:30:01 -0700 In-Reply-To: Mime-Version: 1.0 References: Message-ID: Subject: Re: [PATCH v5 1/6] mm/gup: remove unused vmas parameter from get_user_pages() From: Sean Christopherson To: David Hildenbrand Cc: Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Matthew Wilcox , x86@kernel.org, linux-sgx@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, kvm@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Jarkko Sakkinen , "H . Peter Anvin" , Xinhui Pan , David Airlie , Daniel Vetter , Dimitri Sivanich , Arnd Bergmann , Greg Kroah-Hartman , Paolo Bonzini , Jens Axboe , Pavel Begunkov , Jason Gunthorpe , John Hubbard , Christian Konig , Jason Gunthorpe Content-Type: text/plain; charset="us-ascii" X-Stat-Signature: w7qpuw963bwuw4h99ne9cb4rnhywpk97 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 10183120017 X-Rspam-User: X-HE-Tag: 1684247403-963483 X-HE-Meta: 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 czFvSbCp 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, May 16, 2023, David Hildenbrand wrote: > On 15.05.23 21:07, Sean Christopherson wrote: > > On Sun, May 14, 2023, Lorenzo Stoakes wrote: > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > > index cb5c13eee193..eaa5bb8dbadc 100644 > > > --- a/virt/kvm/kvm_main.c > > > +++ b/virt/kvm/kvm_main.c > > > @@ -2477,7 +2477,7 @@ static inline int check_user_page_hwpoison(unsigned long addr) > > > { > > > int rc, flags = FOLL_HWPOISON | FOLL_WRITE; > > > - rc = get_user_pages(addr, 1, flags, NULL, NULL); > > > + rc = get_user_pages(addr, 1, flags, NULL); > > > return rc == -EHWPOISON; > > > > Unrelated to this patch, I think there's a pre-existing bug here. If gup() returns > > a valid page, KVM will leak the refcount and unintentionally pin the page. That's > > When passing NULL as "pages" to get_user_pages(), __get_user_pages_locked() > won't set FOLL_GET. As FOLL_PIN is also not set, we won't be messing with > the mapcount of the page. Ah, that's what I'm missing. > So even if get_user_pages() returns "1", we should be fine. > > > Or am I misunderstanding your concern? Nope, you covered everything. I do think we can drop the extra gup() though, AFAICT it's 100% redundant. But it's not a bug. Thanks!