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

From: Daniel Borkmann
Date: Thu Mar 09 2017 - 09:02:00 EST

On 03/09/2017 02:10 PM, Thomas Gleixner wrote:
On Thu, 9 Mar 2017, Daniel Borkmann wrote:
With regard to CPA_FLUSHTLB that Linus mentioned, when I investigated
code paths in change_page_attr_set_clr(), I did see that CPA_FLUSHTLB
was set each time we switched attrs and a cpa_flush_range() was
performed (with the correct number of pages and cache set to 0). That
would be a __flush_tlb_all() eventually.

Hmm, it indeed might seem likely that this could be an emulation bug.

Which variant of __flush_tlb_all() is used when the test fails?

Check for the following flags in /proc/cpuinfo: pge invpcid

I added the following and booted with both variants:

printk("X86_FEATURE_PGE:%u\n", static_cpu_has(X86_FEATURE_PGE));
printk("X86_FEATURE_INVPCID:%u\n", static_cpu_has(X86_FEATURE_INVPCID));

"-cpu host" gives:

[ 8.326117] X86_FEATURE_PGE:1
[ 8.326381] X86_FEATURE_INVPCID:1

"-cpu kvm64" gives:

[ 8.517069] X86_FEATURE_PGE:1
[ 8.517393] X86_FEATURE_INVPCID:0