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| author | Sean Christopherson <sean.j.christopherson@intel.com> | 2019-01-25 07:40:48 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-03-23 20:11:40 +0100 |
| commit | cf8d03a4fe59ae40a6a8e5b0925425ef975a5597 (patch) | |
| tree | eb811274c9068ba9ff15f6ab257e273a0dca4f52 /arch/x86 | |
| parent | e1bdcf061b48dafc0755dd2f68fb0e31ed6f2597 (diff) | |
| download | talos-obmc-linux-cf8d03a4fe59ae40a6a8e5b0925425ef975a5597.tar.gz talos-obmc-linux-cf8d03a4fe59ae40a6a8e5b0925425ef975a5597.zip | |
KVM: VMX: Compare only a single byte for VMCS' "launched" in vCPU-run
commit 61c08aa9606d4e48a8a50639c956448a720174c3 upstream.
The vCPU-run asm blob does a manual comparison of a VMCS' launched
status to execute the correct VM-Enter instruction, i.e. VMLAUNCH vs.
VMRESUME. The launched flag is a bool, which is a typedef of _Bool.
C99 does not define an exact size for _Bool, stating only that is must
be large enough to hold '0' and '1'. Most, if not all, compilers use
a single byte for _Bool, including gcc[1].
Originally, 'launched' was of type 'int' and so the asm blob used 'cmpl'
to check the launch status. When 'launched' was moved to be stored on a
per-VMCS basis, struct vcpu_vmx's "temporary" __launched flag was added
in order to avoid having to pass the current VMCS into the asm blob.
The new '__launched' was defined as a 'bool' and not an 'int', but the
'cmp' instruction was not updated.
This has not caused any known problems, likely due to compilers aligning
variables to 4-byte or 8-byte boundaries and KVM zeroing out struct
vcpu_vmx during allocation. I.e. vCPU-run accesses "junk" data, it just
happens to always be zero and so doesn't affect the result.
[1] https://gcc.gnu.org/ml/gcc-patches/2000-10/msg01127.html
Fixes: d462b8192368 ("KVM: VMX: Keep list of loaded VMCSs, instead of vcpus")
Cc: <stable@vger.kernel.org>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/kvm/vmx/vmx.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 30a6bcd735ec..b440b4539969 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6399,7 +6399,7 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx) "mov %%" _ASM_AX", %%cr2 \n\t" "3: \n\t" /* Check if vmlaunch or vmresume is needed */ - "cmpl $0, %c[launched](%%" _ASM_CX ") \n\t" + "cmpb $0, %c[launched](%%" _ASM_CX ") \n\t" /* Load guest registers. Don't clobber flags. */ "mov %c[rax](%%" _ASM_CX "), %%" _ASM_AX " \n\t" "mov %c[rbx](%%" _ASM_CX "), %%" _ASM_BX " \n\t" |
