Re: [PATCH 1/4] hugetlbfs: add arch_hugetlb_valid_size

[Dave Hansen]

On 3/26/20 2:56 PM, Mike Kravetz wrote:
> Perhaps it would be best to check hugepages_supported() when parsing
> hugetlb command line options.  If not enabled, throw an error.  This
> will be much easier to do after moving all command line parsing to
> arch independent code.

Yeah, that sounds sane.

> Is that a sufficient way to address this concern?  I think it is a good
> change in any case.

(Thanks to Kirill for pointing this out.)

So, it turns out the x86 huge page enumeration is totally buggered.
X86_FEATURE_PSE is actually meaningless on 64-bit (and 32-bit PAE).  All
CPUs architecturally support 2MB pages regardless of X86_FEATURE_PSE and
the state of CR4.PSE.

So, on x86_64 at least, hugepages_supported() should *always* return 1.

1GB page support can continue to be dependent on X86_FEATURE_GBPAGES.