On 2/6/19 5:52 AM, Kirill A. Shutemov wrote:
> RDMSR in the trampoline code overrides EDX, but we use the register to
> indicate if 5-level paging has to enabled. It leads to failure to boot
> on a 5-level paging machine.
>
> Preserve EDX on the stack while we are dealing with EFER.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
> Fixes: b677dfae5aa1 ("x86/boot/compressed/64: Set EFER.LME=1 in 32-bit
> trampoline before returning to long mode")
> Reported-by: Kyle D Pelton <kyle.d.pel...@intel.com>
> Cc: Wei Huang <w...@redhat.com>
> ---
> arch/x86/boot/compressed/head_64.S | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/boot/compressed/head_64.S
> b/arch/x86/boot/compressed/head_64.S
> index f105ae8651c9..f62e347862cc 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -602,10 +602,12 @@ ENTRY(trampoline_32bit_src)
> 3:
> /* Set EFER.LME=1 as a precaution in case hypervsior pulls the rug */
> pushl %ecx
> + pushl %edx
> movl $MSR_EFER, %ecx
> rdmsr
> btsl $_EFER_LME, %eax
> wrmsr
> + popl %edx
> popl %ecx
>
> /* Enable PAE and LA57 (if required) paging modes */
>
Oops, rdmsr indeed corrupts EDX.
Acked-by: Wei Huang <w...@redhat.com>
