On Thu, Aug 14, 2025 at 11:59:01AM +1200, Kai Huang wrote:
> During kexec, the kernel jumps to the new kernel in relocate_kernel(),
> which is implemented in assembly and both 32-bit and 64-bit have their
> own version.
>
> Currently, for both 32-bit and 64-bit, the last two parameters of the
> relocate_kernel() are both 'unsigned int' but actually they only convey
> a boolean, i.e., one bit information. The 'unsigned int' has enough
> space to carry two bits information therefore there's no need to pass
> the two booleans in two separate 'unsigned int'.
>
> Consolidate the last two function parameters of relocate_kernel() into a
> single 'unsigned int' and pass flags instead.
>
> Only consolidate the 64-bit version albeit the similar optimization can
> be done for the 32-bit version too. Don't bother changing the 32-bit
> version while it is working (since assembly code change is required).
>
> Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
>
> v5 -> v6:
> - Add Tom's RB.
>
> v4 -> v5:
> - RELOC_KERNEL_HOST_MEM_ACTIVE -> RELOC_KERNEL_HOST_MEM_ENC_ACTIVE
> (Tom)
> - Add a comment to explain only RELOC_KERNEL_PRESERVE_CONTEXT is
> restored after jumping back from peer kernel for preserved_context
> kexec (pointed out by Tom).
> - Use testb instead of testq when comparing the flag with R11 to save
> 3 bytes (Hpa).
>
> v4:
> - new patch
>
>
> ---
> arch/x86/include/asm/kexec.h | 12 ++++++++++--
> arch/x86/kernel/machine_kexec_64.c | 22 +++++++++++++---------
> arch/x86/kernel/relocate_kernel_64.S | 25 +++++++++++++++----------
> 3 files changed, 38 insertions(+), 21 deletions(-)
Reviewed-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
