On 08.08.2025 22:23, Andrew Cooper wrote: > FRED and IDT differ by a Supervisor Token on the base of the shstk. This > means that the value they load into MSR_PL0_SSP differs by 8. > > s3_resume() in particular has logic which is otherwise invariant of FRED mode, > and must not clobber a FRED MSR_PL0_SSP with an IDT one. > > This also simplifies the AP path too. Updating reinit_bsp_stack() is deferred > until later. > > No functional change. > > Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
I wonder why this was originally done in assembly in the first place, when we aim at reducing tghe assembly code we have. > --- a/xen/arch/x86/boot/x86_64.S > +++ b/xen/arch/x86/boot/x86_64.S > @@ -65,17 +65,11 @@ ENTRY(__high_start) > or $(PRIMARY_SHSTK_SLOT + 1) * PAGE_SIZE - 8, %rdx > > /* > - * Write a new supervisor token. Doesn't matter on boot, but for S3 > - * resume this clears the busy bit. > + * Write a new Supervisor Token. It doesn't matter the first time a > + * CPU boots, but for S3 resume or CPU hot re-add, this clears the > + * busy bit. > */ > wrssq %rdx, (%rdx) > - > - /* Point MSR_PL0_SSP at the token. */ > - mov $MSR_PL0_SSP, %ecx > - mov %edx, %eax > - shr $32, %rdx > - wrmsr > - > setssbsy This is ending up a little odd: The comment says the write is to clear the busy bit, when that's re-set immediately afterwards. Jan
