Re: [PATCH 1/2] x86/kexec: Preserve CR4.MCE during kexec

[Kirill A. Shutemov]

On Thu, Feb 16, 2023 at 01:49:39AM +0000, Edgecombe, Rick P wrote:
> On Tue, 2023-02-14 at 02:48 +0300, Kirill A. Shutemov wrote:
> > TDX guests are not allowed to clear CR4.MCE. Attempt to clear it
> > leads
> > to #VE.
> > 
> > Preserve the flag during kexec.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> 
> I wonder whats going on with the pre-existing switching between eax and
> rax in this code for the cr0 and cr4 manipulations. Do you know what
> the reason is?

32-bit ORs and ANDs save one byte per instruction. And there's no 32-bit
MOV to/from control registers in 64-bit mode.

> 
> Also, for a simple non-tdx kexec regression test:
> Tested-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>

Thanks!

-- 
  Kiryl Shutsemau / Kirill A. Shutemov