From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f72.google.com (mail-oi0-f72.google.com [209.85.218.72]) by kanga.kvack.org (Postfix) with ESMTP id E9E436B0003 for ; Thu, 1 Feb 2018 10:33:29 -0500 (EST) Received: by mail-oi0-f72.google.com with SMTP id 1so11616601oiq.8 for ; Thu, 01 Feb 2018 07:33:29 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id p3si6540559ote.143.2018.02.01.07.33.28 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Feb 2018 07:33:28 -0800 (PST) Date: Thu, 1 Feb 2018 16:33:10 +0100 From: Radim =?utf-8?B?S3LEjW3DocWZ?= Subject: Re: [PATCH] KVM/x86: remove WARN_ON() for when vm_munmap() fails Message-ID: <20180201153310.GD31080@flask> References: <001a1141c71c13f559055d1b28eb@google.com> <20180201013021.151884-1-ebiggers3@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180201013021.151884-1-ebiggers3@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Eric Biggers Cc: kvm@vger.kernel.org, Paolo Bonzini , linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Eric Biggers 2018-01-31 17:30-0800, Eric Biggers: > From: Eric Biggers > > On x86, special KVM memslots such as the TSS region have anonymous > memory mappings created on behalf of userspace, and these mappings are > removed when the VM is destroyed. > > It is however possible for removing these mappings via vm_munmap() to > fail. This can most easily happen if the thread receives SIGKILL while > it's waiting to acquire ->mmap_sem. This triggers the 'WARN_ON(r < 0)' > in __x86_set_memory_region(). syzkaller was able to hit this, using > 'exit()' to send the SIGKILL. Note that while the vm_munmap() failure > results in the mapping not being removed immediately, it is not leaked > forever but rather will be freed when the process exits. > > It's not really possible to handle this failure properly, so almost We could check "r < 0 && r != -EINTR" to get rid of the easily triggerable warning. > every other caller of vm_munmap() doesn't check the return value. It's > a limitation of having the kernel manage these mappings rather than > userspace. > > So just remove the WARN_ON() so that users can't spam the kernel log > with this warning. > > Fixes: f0d648bdf0a5 ("KVM: x86: map/unmap private slots in __x86_set_memory_region") > Reported-by: syzbot > Signed-off-by: Eric Biggers > --- Removing it altogether doesn't sound that bad, though ... Queued, thanks. > arch/x86/kvm/x86.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index c53298dfbf50..53b57f18baec 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -8272,10 +8272,8 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size) > return r; > } > > - if (!size) { > - r = vm_munmap(old.userspace_addr, old.npages * PAGE_SIZE); > - WARN_ON(r < 0); > - } > + if (!size) > + vm_munmap(old.userspace_addr, old.npages * PAGE_SIZE); > > return 0; > } > -- > 2.16.0.rc1.238.g530d649a79-goog > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org