On Fri, 2015-05-22 at 10:34 +0200, Thomas Gleixner wrote:
> On Wed, 13 May 2015, Toshi Kani wrote:
>
> > --- a/arch/x86/mm/pat.c
> > +++ b/arch/x86/mm/pat.c
> > @@ -182,7 +182,11 @@ void pat_init_cache_modes(void)
> > char pat_msg[33];
> > u64 pat;
> >
> > - rdmsrl(MSR_IA32_CR_PAT, pat);
> > + if (pat_enabled)
> > + rdmsrl(MSR_IA32_CR_PAT, pat);
> > + else
> > + pat = boot_pat_state;
>
> boot_pat_state is 0 if pat is disabled, but this boot_pat_state multi
> purpose usage is really horrible. We do 5 things at once with it and
> of course all of it completely undocumented.
boot_pat_state is set even if pat is disabled so that this case can be
handled in the same framework.
:
if (!pat_enabled) {
/*
* No PAT. Emulate the PAT table that corresponds to the two
:
pat = PAT(0, WB) | PAT(1, WT) | PAT(2, UC_MINUS) | PAT(3, UC) |
PAT(4, WB) | PAT(5, WT) | PAT(6, UC_MINUS) | PAT(7, UC);
if (!boot_pat_state)
boot_pat_state = pat;
:
That said, yes, I agree that the use of boot_pat_state is overloaded.
> pat_msg[32] = 0;
> > for (i = 7; i >= 0; i--) {
> > cache = pat_get_cache_mode((pat >> (i * 8)) & 7,
> > @@ -200,28 +204,58 @@ void pat_init(void)
> > bool boot_cpu = !boot_pat_state;
>
> The crap starts here and this really wants to be distangled.
Agreed.
> void pat_init(void)
> {
> static bool boot_done;
>
> if (!boot_done) {
> if (!cpu_has_pat)
> pat_disable("PAT not supported by CPU.");
>
> if (pat_enabled) {
> rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
> if (!boot_pat_state)
> pat_disable("PAT read returns always zero,
> disabled.");
> }
> } else if (!cpu_has_pat && pat_enabled) {
> /*
> * If this happens we are on a secondary CPU, but
> * switched to PAT on the boot CPU. We have no way to
> * undo PAT.
> */
> pr_err("PAT enabled but not supported by secondary CPU\n");
> BUG();
> }
>
>
> if (!pat_enabled) {
> .....
> } else {
> .....
> }
>
> if (!boot_done) {
> ....
> boot_done = true;
> }
> }
>
> And this cleanup wants to be done as a seperate patch before you do
> this other stuff.
Yes, this looks much better! Will add a patch for this clean up.
> > @@ -275,16 +309,8 @@ void pat_init(void)
> > PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, WT);
> > }
> >
> > - /* Boot CPU check */
> > - if (!boot_pat_state) {
> > - rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
> > - if (!boot_pat_state) {
> > - pat_disable("PAT read returns always zero, disabled.");
> > - return;
> > - }
> > - }
> > -
> > - wrmsrl(MSR_IA32_CR_PAT, pat);
> > + if (pat_enabled)
> > + wrmsrl(MSR_IA32_CR_PAT, pat);
>
> Sigh.
Yeah...
>
> if (!pat_enabled) {
> ....
> } else {
> ....
> }
>
> + if (pat_enabled)
>
> Thanks,
Thanks a lot!
-Toshi
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