KVM: nVMX: Check a single byte for VMCS "launched" in nested early checks

Nested early checks does a manual comparison of a VMCS' launched status
in its asm blob 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].

The use of 'cmpl' instead of 'cmpb' was not deliberate, but rather the
result of a copy-paste as the asm blob was directly derived from the asm
blob for vCPU-run.

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: 52017608da33 ("KVM: nVMX: add option to perform early consistency checks via H/W")
Cc: <[email protected]>
Reviewed-by: Jim Mattson <[email protected]>
Reviewed-by: Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

0 files changed, 0 insertions, 0 deletions