Re: [PATCH 04/23] x86, tlb: make CR4-based TLB flushes more robust

[Andy Lutomirski]

On Wed, Nov 1, 2017 at 3:11 AM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
> On Wed, Nov 01, 2017 at 01:01:45AM -0700, Andy Lutomirski wrote:
>> On Tue, Oct 31, 2017 at 3:31 PM, Dave Hansen
>> <dave.hansen@xxxxxxxxxxxxxxx> wrote:
>> >
>> > Our CR4-based TLB flush currently requries global pages to be
>> > supported *and* enabled.  But, we really only need for them to be
>> > supported.  Make the code more robust by alllowing X86_CR4_PGE to
>> > clear as well as set.
>> >
>> > This change was suggested by Kirill Shutemov.
>>
>> I may have missed something, but why would be ever have CR4.PGE off?
>
> This came out from me thinking on if we can disable global pages by not
> turning on CR4.PGE instead of making _PAGE_GLOBAL zero.
>
> Dave decided to not take this path, but this change would make
> __native_flush_tlb_global_irq_disabled() a bit less fragile in case
> if the situation would change in the future.

How about just adding a VM_WARN_ON_ONCE, then?

--Andy