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 switch_stack_and_jump() needs to discard one extra word when FRED
> is active.
>
> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
> ---
> CC: Jan Beulich <jbeul...@suse.com>
> CC: Roger Pau Monné <roger....@citrix.com>
>
> RFC. I don't like this, but it does work.
>
> This emits opt_fred logic outside of CONFIG_XEN_SHSTK.
opt_fred and XEN_SHSTK are orthogonal, so that's fine anyway. What I guess
you may mean is that you now have a shstk-related calculation outside of
a respective #ifdef. Given the simplicity of the calculation, ...
> But frankly, the
> construct is already too unweildly, and all options I can think of make it
> moreso.
... I agree having it like this is okay.
> @@ -154,7 +155,6 @@ unsigned long get_stack_dump_bottom (unsigned long sp);
> "rdsspd %[ssp];" \
> "cmp $1, %[ssp];" \
> "je .L_shstk_done.%=;" /* CET not active? Skip. */ \
> - "mov $%c[skstk_base], %[val];" \
> "and $%c[stack_mask], %[ssp];" \
> "sub %[ssp], %[val];" \
> "shr $3, %[val];" \
With the latter two insns here, ...
> @@ -177,6 +177,8 @@ unsigned long get_stack_dump_bottom (unsigned long sp);
>
> #define switch_stack_and_jump(fn, instr, constr) \
> ({ \
> + unsigned int token_offset = \
> + (PRIMARY_SHSTK_SLOT + 1) * PAGE_SIZE - (opt_fred ? 0 : 8); \
> unsigned int tmp; \
> BUILD_BUG_ON(!ssaj_has_attr_noreturn(fn)); \
> __asm__ __volatile__ ( \
> @@ -184,12 +186,11 @@ unsigned long get_stack_dump_bottom (unsigned long sp);
> "mov %[stk], %%rsp;" \
> CHECK_FOR_LIVEPATCH_WORK \
> instr "[fun]" \
> - : [val] "=&r" (tmp), \
> + : [val] "=r" (tmp), \
... I don't think you can legitimately drop the & from here? With it
retained:
Reviewed-by: Jan Beulich <jbeul...@suse.com>
Jan
