This is a note to let you know that I've just added the patch titled KVM: nVMX: Fix handling of lmsw instruction to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-nvmx-fix-handling-of-lmsw-instruction.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Tue Apr 10 10:31:53 CEST 2018 From: "Jan H. Schönherr" <jschoenh@xxxxxxxxx> Date: Sat, 20 May 2017 13:22:56 +0200 Subject: KVM: nVMX: Fix handling of lmsw instruction From: "Jan H. Schönherr" <jschoenh@xxxxxxxxx> [ Upstream commit e1d39b17e044e8ae819827810d87d809ba5f58c0 ] The decision whether or not to exit from L2 to L1 on an lmsw instruction is based on bogus values: instead of using the information encoded within the exit qualification, it uses the data also used for the mov-to-cr instruction, which boils down to using whatever is in %eax at that point. Use the correct values instead. Without this fix, an L1 may not get notified when a 32-bit Linux L2 switches its secondary CPUs to protected mode; the L1 is only notified on the next modification of CR0. This short time window poses a problem, when there is some other reason to exit to L1 in between. Then, L2 will be resumed in real mode and chaos ensues. Signed-off-by: Jan H. Schönherr <jschoenh@xxxxxxxxx> Reviewed-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kvm/vmx.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -7657,11 +7657,13 @@ static bool nested_vmx_exit_handled_cr(s { unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION); int cr = exit_qualification & 15; - int reg = (exit_qualification >> 8) & 15; - unsigned long val = kvm_register_readl(vcpu, reg); + int reg; + unsigned long val; switch ((exit_qualification >> 4) & 3) { case 0: /* mov to cr */ + reg = (exit_qualification >> 8) & 15; + val = kvm_register_readl(vcpu, reg); switch (cr) { case 0: if (vmcs12->cr0_guest_host_mask & @@ -7716,6 +7718,7 @@ static bool nested_vmx_exit_handled_cr(s * lmsw can change bits 1..3 of cr0, and only set bit 0 of * cr0. Other attempted changes are ignored, with no exit. */ + val = (exit_qualification >> LMSW_SOURCE_DATA_SHIFT) & 0x0f; if (vmcs12->cr0_guest_host_mask & 0xe & (val ^ vmcs12->cr0_read_shadow)) return true; Patches currently in stable-queue which might be from jschoenh@xxxxxxxxx are queue-4.4/kvm-nvmx-fix-handling-of-lmsw-instruction.patch