On Tue, Nov 19, 2024 at 04:35:00PM +0100, Valentin Schneider wrote:
> +void noinstr __flush_tlb_all_noinstr(void)
> +{
> + /*
> + * This is for invocation in early entry code that cannot be
> + * instrumented. A RMW to CR4 works for most cases, but relies on
> + * being able to flip either of the PGE or PCIDE bits. Flipping CR4.PCID
> + * would require also resetting CR3.PCID, so just try with CR4.PGE, else
> + * do the CR3 write.
> + *
> + * XXX: this gives paravirt the finger.
> + */
> + if (cpu_feature_enabled(X86_FEATURE_PGE))
> + __native_tlb_flush_global_noinstr(this_cpu_read(cpu_tlbstate.cr4));
> + else
> + native_flush_tlb_local_noinstr();
> +}
Urgh, so that's a lot of ugleh, and cr4 has that pinning stuff and gah.
Why not always just do the CR3 write and call it a day? That should also
work for paravirt, no? Just make the whole write_cr3 thing noinstr and
voila.
