On July 21, 2025 4:42:22 PM PDT, "Huang, Kai" <kai.huang@xxxxxxxxx> wrote: >On Mon, 2025-07-21 at 23:29 +0000, Huang, Kai wrote: >> > On July 21, 2025 2:36:48 PM PDT, "Huang, Kai" <kai.huang@xxxxxxxxx> wrote: >> > > On Mon, 2025-07-21 at 16:27 -0500, Tom Lendacky wrote: >> > > > > > > @@ -204,7 +202,7 @@ >> > SYM_CODE_START_LOCAL_NOALIGN(identity_mapped) >> > > > > > > * entries that will conflict with the now unencrypted memory >> > > > > > > * used by kexec. Flush the caches before copying the kernel. >> > > > > > > */ >> > > > > > > - testq %r8, %r8 >> > > > > > > + testq $RELOC_KERNEL_HOST_MEM_ACTIVE, %r11 >> > > > > > >> > > > > > Hmmm... can't both bits be set at the same time? If so, then this >> > > > > > will fail. This should be doing bit tests now. >> > > > > >> > > > > TEST instruction performs logical AND of the two operands, >> > > > > therefore the above equals to: >> > > > > >> > > > > set ZF if "R11 AND BIT(1) == 0". >> > > > > >> > > > > Whether there's any other bits set in R11 doesn't impact the above, right? >> > > > > >> > > > >> > > > Doh! My bad, yes, not sure what I was thinking there. >> > > > >> > > >> > > Np and thanks! I'll address your other comments but I'll see whether >> > > Boris has any other comments first. >> > > >> > >> > You can use testb in this case to save 3 bytes, too. >> >> Yeah I can do that, thanks for the info! > >I just tried. I need to do: > > testb $RELOC_KERNEL_HOST_MEM_ACTIVE, %r11b > >in order to compile, otherwise using plain %r11 generates: > >arch/x86/kernel/relocate_kernel_64.S:212: Error: `%r11' not allowed with >`testb' > >I'll do some test and if there's no problem I'll switch to use this way, >assuming it still saves us 3-bytes. > That works just fine.
