On Thu, Jun 08, 2023 at 04:03:33PM +0200, Juergen Gross wrote:
> Instead of stacking alternative and paravirt patching, use the new
> ALT_FLAG_CALL flag to switch those mixed calls to pure alternative
> handling.
>
> This eliminates the need to be careful regarding the sequence of
> alternative and paravirt patching.
>
> For call depth tracking callthunks_setup() needs to be adapted to patch
> calls at alternative patching sites instead of paravirt calls.
>
> Remove the no longer needed paravirt patching and related code.
I think this becomes easier if you first convert the paravirt sites to
alternatives, such that .parainstructions is empty, and then in a
subsequent patch remove all the paravirt infrastructure that is unused.
> +#define SAVE_FLAGS ALTERNATIVE_2 "PARA_IRQ_save_fl;", ALT_CALL_INSTR, \
> + ALT_CALL_ALWAYS, "pushf; pop %rax;", \
> + ALT_NOT(X86_FEATURE_XENPV)
I find this more readable when written as:
#define SAVE_FLAGS ALTERNATIVE_2 "PARA_IRQ_save_fl;", \
ALT_CALL_INSTR, ALT_CALL_ALWAYS, \
"pushf; pop %rax;", ALT_NOT(X86_FEATURE_XENPV)
(and perhaps ALT_NOT_XEN is in order, there's a ton of those)
If you base this on top of the nested alternative patches, another
helper might be:
#define __PV_ALTERNATIVE(old) __ALTERNATIVE(old, ALT_CALL_INSTR, ALT_CALL_ALWAYS)
So that you can then write:
#define SAVE_FLAGS __ALTERNATIVE(__PV_ALTERNATIVE("PARA_IRQ_save_fl;"),
"pushf; pop %rax;", ALT_NOT_XEN)
But perhaps I'm over-cooking things now..
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