Messages in this thread | | | Date | Fri, 5 May 2017 11:20:46 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v3 2/2] x86_64/kexec: Use PUD level 1GB page for identity mapping if available |
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* Xunlei Pang <xpang@redhat.com> wrote:
> On 05/05/2017 at 02:52 PM, Ingo Molnar wrote: > > * Xunlei Pang <xlpang@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
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