Re: FAILED: patch "[PATCH] KVM: x86: Fix potential put_fpu() w/o load_fpu() on MPX" failed to apply to 4.14-stable tree

[Sasha Levin <sashal@kernel.org>]

On Sun, Feb 09, 2020 at 01:22:44PM +0100, gregkh@linuxfoundation.org wrote:
>
>The patch below does not apply to the 4.14-stable tree.
>If someone wants it applied there, or to any other stable or longterm
>tree, then please email the backport, including the original git commit
>id to <stable@vger.kernel.org>.
>
>thanks,
>
>greg k-h
>
>------------------ original commit in Linus's tree ------------------
>
>From f958bd2314d117f8c29f4821401bc1925bc2e5ef Mon Sep 17 00:00:00 2001
>From: Sean Christopherson <sean.j.christopherson@intel.com>
>Date: Mon, 9 Dec 2019 12:19:31 -0800
>Subject: [PATCH] KVM: x86: Fix potential put_fpu() w/o load_fpu() on MPX
> platform
>
>Unlike most state managed by XSAVE, MPX is initialized to zero on INIT.
>Because INITs are usually recognized in the context of a VCPU_RUN call,
>kvm_vcpu_reset() puts the guest's FPU so that the FPU state is resident
>in memory, zeros the MPX state, and reloads FPU state to hardware.  But,
>in the unlikely event that an INIT is recognized during
>kvm_arch_vcpu_ioctl_get_mpstate() via kvm_apic_accept_events(),
>kvm_vcpu_reset() will call kvm_put_guest_fpu() without a preceding
>kvm_load_guest_fpu() and corrupt the guest's FPU state (and possibly
>userspace's FPU state as well).
>
>Given that MPX is being removed from the kernel[*], fix the bug with the
>simple-but-ugly approach of loading the guest's FPU during
>KVM_GET_MP_STATE.
>
>[*] See commit f240652b6032b ("x86/mpx: Remove MPX APIs").
>
>Fixes: f775b13eedee2 ("x86,kvm: move qemu/guest FPU switching out to vcpu_run")
>Cc: stable@vger.kernel.org
>Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
>Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

The conflict is because we didn't have fd2325612c14 ("KVM: Move
vcpu_load to arch-specific kvm_arch_vcpu_ioctl_get_mpstate") on older
kernels. I've fixed it and queued for 4.14.

-- 
Thanks,
Sasha