* Bryan O'Donoghue <pure.lo...@nexus-software.ie> wrote:
> >>diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> >>index 41ead8d..1d2396a 100644
> >>--- a/arch/x86/kernel/setup.c
> >>+++ b/arch/x86/kernel/setup.c
> >>@@ -879,7 +879,10 @@ void __init setup_arch(char **cmdline_p)
> >> KERNEL_PGD_PTRS);
> >>
> >> load_cr3(swapper_pg_dir);
> >>- __flush_tlb_all();
> >>+ if (boot_cpu_data.x86 == 5 && boot_cpu_data.x86_model == 9)
> >>+ __flush_tlb();
> >>+ else
> >>+ __flush_tlb_all();
> >
> >So why not make __flush_tlb_all() Quark-quirk-aware and be done
> >with it, instead of having to validate every single
> >__flush_tlb_all() user?
> >
> >Quark breaks the x86 'flush all TLBs' semantics - the way to fix
> >it is to restore those semantics, not to sprinkle the breakage
> >all around the code ...
>
> Hi Ingo.
>
> We have made __flush_tlb_all() Quark aware - because the previous patch we
> applied to arch/x86/kernel/cpu/intel.c
>
> ee1b5b165c0a2f04d2107e634e51f05d0eb107de
>
> + if (c->x86 == 5 && c->x86_model == 9) {
> + pr_info("Disabling PGE capability bit\n");
> + setup_clear_cpu_cap(X86_FEATURE_PGE);
> + }
>
> will cause cpu_has_pge() to be false and then the flush_tlb_all code will
> take the path we want __flush_tlb not __flush_tlb_global
>
> static inline void __flush_tlb_all(void)
> {
> if (cpu_has_pge)
> __flush_tlb_global();
> else
> __flush_tlb();
> }
>
> The code in setup_arch runs before the cpu_has_pge bit been clobbered.
So why is the comment in setup_arch() not talking about that?
> The commit you did 02276a3a677d681f0cd227d7111c71fdbce23832 just adds a
> comment to setup_arch to indicate the behaviour we are relying on
>
> setup_arch()
> {
>
> load_cr3(swapper_pg_dir); /* this will flush the TLB on Quark */
> __flush_tlb_all(); /*cpu_has_pge() is true at this point*/
>
> ......
>
> /* this is where we latch the cpu cabability bits */
> early_cpu_init();
> }
I've zapped that commit for the time being, because I think that
at minimum the comment is misleading - it says nothing about this
being an early quirk and that normally __flush_tlb_all() will
DTRT.
It talks about:
+ /*
+ * Locate the page directory and flush the TLB.
+ * On Quark X1000 rewriting CR3 flushes the TLB no if/else is required
+ * to choose between __flush_tlb() and __flush_tlb_all()
+ */
load_cr3(swapper_pg_dir);
__flush_tlb_all();
But it is completely silent on the real reason for why we don't
need a Quark quirk here, which would be something like:
/*
* On Quark CPUs we still have the PGE bit set so
* __flush_tlb_all() is not yet doing what it says - but
* accidentally we have a cr3 flush here which is what is
* needed - so there's no need to add a Quark quirk here.
*/
Right?
Thanks,
Ingo
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