* Xunlei Pang <xpang at redhat.com> wrote:
> On 05/05/2017 at 02:52 PM, Ingo Molnar wrote:
> > * Xunlei Pang <xlpang at redhat.com> wrote:
> >
> >> @@ -122,6 +122,10 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
> >>
> >> level4p = (pgd_t *)__va(start_pgtable);
> >> clear_page(level4p);
> >> +
> >> + if (direct_gbpages)
> >> + info.direct_gbpages = true;
> > No, this should be keyed off the CPU feature (X86_FEATURE_GBPAGES) automatically,
> > not set blindly! AFAICS this patch will crash kexec on any CPU that does not
> > support gbpages.
>
> It should be fine, probe_page_size_mask() already takes care of this:
> if (direct_gbpages && boot_cpu_has(X86_FEATURE_GBPAGES)) {
> printk(KERN_INFO "Using GB pages for direct mapping\n");
> page_size_mask |= 1 << PG_LEVEL_1G;
> } else {
> direct_gbpages = 0;
> }
>
> So if X86_FEATURE_GBPAGES is not supported, direct_gbpages will be set to 0.
So why is the introduction of the info.direct_gbpages flag necessary? AFAICS it
just duplicates the kernel's direct_gbpages flag. One outcome is that hibernation
won't use gbpages, which is silly.
Thanks,
Ingo
