This is a note to let you know that I've just added the patch titled
KVM: nVMX: do not warn when MSR bitmap address is not backed
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: kvm-nvmx-do-not-warn-when-msr-bitmap-address-is-not-backed.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Mon Dec 18 14:12:34 CET 2017
From: Radim Krčmář rkrcmar@redhat.com Date: Tue, 7 Mar 2017 17:51:49 +0100 Subject: KVM: nVMX: do not warn when MSR bitmap address is not backed
From: Radim Krčmář rkrcmar@redhat.com
[ Upstream commit 05d8d34611139f8435af90ac54b65eb31e82e388 ]
Before trying to do nested_get_page() in nested_vmx_merge_msr_bitmap(), we have already checked that the MSR bitmap address is valid (4k aligned and within physical limits). SDM doesn't specify what happens if the there is no memory mapped at the valid address, but Intel CPUs treat the situation as if the bitmap was configured to trap all MSRs.
KVM already does that by returning false and a correct handling doesn't need the guest-trigerrable warning that was reported by syzkaller: (The warning was originally there to catch some possible bugs in nVMX.)
------------[ cut here ]------------ WARNING: CPU: 0 PID: 7832 at arch/x86/kvm/vmx.c:9709 nested_vmx_merge_msr_bitmap arch/x86/kvm/vmx.c:9709 [inline] WARNING: CPU: 0 PID: 7832 at arch/x86/kvm/vmx.c:9709 nested_get_vmcs12_pages+0xfb6/0x15c0 arch/x86/kvm/vmx.c:9640 Kernel panic - not syncing: panic_on_warn set ... CPU: 0 PID: 7832 Comm: syz-executor1 Not tainted 4.10.0+ #229 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:15 [inline] dump_stack+0x2ee/0x3ef lib/dump_stack.c:51 panic+0x1fb/0x412 kernel/panic.c:179 __warn+0x1c4/0x1e0 kernel/panic.c:540 warn_slowpath_null+0x2c/0x40 kernel/panic.c:583 nested_vmx_merge_msr_bitmap arch/x86/kvm/vmx.c:9709 [inline] nested_get_vmcs12_pages+0xfb6/0x15c0 arch/x86/kvm/vmx.c:9640 enter_vmx_non_root_mode arch/x86/kvm/vmx.c:10471 [inline] nested_vmx_run+0x6186/0xaab0 arch/x86/kvm/vmx.c:10561 handle_vmlaunch+0x1a/0x20 arch/x86/kvm/vmx.c:7312 vmx_handle_exit+0xfc0/0x3f00 arch/x86/kvm/vmx.c:8526 vcpu_enter_guest arch/x86/kvm/x86.c:6982 [inline] vcpu_run arch/x86/kvm/x86.c:7044 [inline] kvm_arch_vcpu_ioctl_run+0x1418/0x4840 arch/x86/kvm/x86.c:7205 kvm_vcpu_ioctl+0x673/0x1120 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2570
Reported-by: Dmitry Vyukov dvyukov@google.com Reviewed-by: Jim Mattson jmattson@google.com [Jim Mattson explained the bare metal behavior: "I believe this behavior would be documented in the chipset data sheet rather than the SDM, since the chipset returns all 1s for an unclaimed read."] Signed-off-by: Radim Krčmář rkrcmar@redhat.com
Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/vmx.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
--- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -9543,10 +9543,8 @@ static inline bool nested_vmx_merge_msr_ return false;
page = nested_get_page(vcpu, vmcs12->msr_bitmap); - if (!page) { - WARN_ON(1); + if (!page) return false; - } msr_bitmap_l1 = (unsigned long *)kmap(page); if (!msr_bitmap_l1) { nested_release_page_clean(page);
Patches currently in stable-queue which might be from rkrcmar@redhat.com are
queue-4.9/kvm-nvmx-do-not-warn-when-msr-bitmap-address-is-not-backed.patch