Re: [net/bpf] 3051bf36c2 BUG: unable to handle kernel paging request at 0000a7cf

From: Daniel Borkmann
Date: Thu Mar 09 2017 - 13:31:25 EST

On 03/09/2017 07:15 PM, Linus Torvalds wrote:
On Thu, Mar 9, 2017 at 10:10 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

Very odd. We should always have PGE (0x0080) set in cr4 (if the CPU
supports it).

Daniel, do you see the code in probe_page_size_mask() triggering?

/* Enable PGE if available */
if (boot_cpu_has(X86_FEATURE_PGE)) {
__supported_pte_mask |= _PAGE_GLOBAL;

We do have boot_cpu_has(X86_FEATURE_PGE) and go indeed into this
branch here. So it seems something must be clearing it later, hmm.

} else
__supported_pte_mask &= ~_PAGE_GLOBAL;

but maybe there's something wrong with the percpu cr4 caching?