Re: Flushing user entries for kernel mappings in x86

[Nadav Amit]

at 8:45 PM, Andy Lutomirski <luto@xxxxxxxxxx> wrote:

> On Tue, Aug 28, 2018 at 6:46 PM, Nadav Amit <nadav.amit@xxxxxxxxx> wrote:
>> Hello Andy,
>> 
>> Is there a reason for __flush_tlb_one_kernel() to flush the PTE not only in
>> the kernel address space, but also in the user one (as part of
>> __flush_tlb_one_user)? [ I obviously regard the case when PTI is on ].
> 
> In most cases, probably not, but it's fairly cheap, I think.  And it
> makes it so that we're okay if the TLB entry we're flushing is used by
> the entry code.

Thanks. I assumed thatâs the case. I donât know how cheap they are
(especially if INVPCID is not supported) but I guess they are not that
frequent.