On 15/07/20 22:52, Sean Christopherson wrote:
> Explicitly zero cr4 in prepare_64() instead of "zeroing" it in the
> common enter_long_mode(). Clobbering cr4 in enter_long_mode() breaks
> switch_to_5level(), which sets cr4.LA57 before calling enter_long_mode()
> and obviously expects cr4 to be preserved.
>
> Fixes: d86ef58 ("cstart: do not assume CR4 starts as zero")
> Cc: Nadav Amit <namit@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> ---
>
> Two lines of code, two bugs. I'm pretty sure Paolo should win some kind
> of award. :-D
Two lines of code, two bugs immediately before disappearing for two
weeks. 2^3 paper bags...
Paolo
> x86/cstart64.S | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/x86/cstart64.S b/x86/cstart64.S
> index 3ae98d3..2d16688 100644
> --- a/x86/cstart64.S
> +++ b/x86/cstart64.S
> @@ -175,8 +175,12 @@ prepare_64:
> lgdt gdt64_desc
> setup_segments
>
> + xor %eax, %eax
> + mov %eax, %cr4
> +
> enter_long_mode:
> - mov $(1 << 5), %eax // pae
> + mov %cr4, %eax
> + bts $5, %eax // pae
> mov %eax, %cr4
>
> mov pt_root, %eax
>
