From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg Kroah-Hartman Subject: Re: [PATCH] KVM: x86: Fix a 4.14 backport regression related to userspace/guest FPU Date: Tue, 29 Jan 2019 10:42:46 +0100 Message-ID: <20190129094246.GB20645@kroah.com> References: <20190128205102.29393-1-sean.j.christopherson@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: Sasha Levin , kvm@vger.kernel.org, stable@vger.kernel.org, Peter Xu , Rik van Riel , Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Thomas Lindroth To: Sean Christopherson Return-path: Content-Disposition: inline In-Reply-To: <20190128205102.29393-1-sean.j.christopherson@intel.com> Sender: stable-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Mon, Jan 28, 2019 at 12:51:02PM -0800, Sean Christopherson wrote: > Upstream commit: > > f775b13eedee ("x86,kvm: move qemu/guest FPU switching out to vcpu_run") > > introduced a bug, which was later fixed by upstream commit: > > 5663d8f9bbe4 ("kvm: x86: fix WARN due to uninitialized guest FPU state") > > For reasons unknown, both commits were initially passed-over for > inclusion in the 4.14 stable branch despite being tagged for stable. > Eventually, someone noticed that the fixup, commit 5663d8f9bbe4, was > missing from stable[1], and so it was queued up for 4.14 and included in > release v4.14.79. > > Even later, the original buggy patch, commit f775b13eedee, was also > applied to the 4.14 stable branch. Through an unlucky coincidence, the > incorrect ordering did not generate a conflict between the two patches, > and led to v4.14.94 and later releases containing a spurious call to > kvm_load_guest_fpu() in kvm_arch_vcpu_ioctl_run(). As a result, KVM may > reload stale guest FPU state, e.g. after accepting in INIT event. This > can manifest as crashes during boot, segfaults, failed checksums and so > on and so forth. > > Remove the unwanted kvm_{load,put}_guest_fpu() calls, i.e. make > kvm_arch_vcpu_ioctl_run() look like commit 5663d8f9bbe4 was backported > after commit f775b13eedee. > > [1] https://www.spinics.net/lists/stable/msg263931.html > > Fixes: 4124a4cff344 ("x86,kvm: move qemu/guest FPU switching out to vcpu_run") > Cc: stable@vger.kernel.org > Cc: Sasha Levin > Cc: Greg Kroah-Hartman > Cc: Peter Xu > Cc: Rik van Riel > Cc: Paolo Bonzini > Cc: Radim Krčmář > Reported-by: Roman Mamedov > Reported-by: Thomas Lindroth > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/x86.c | 6 +----- > 1 file changed, 1 insertion(+), 5 deletions(-) Thanks so much for this, sorry for the mis-merge, nice catch! Now queued up. greg k-h