Messages in this thread | | | Date | Tue, 14 Jul 2020 21:49:21 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH 12/15] kmap: Add stray write protection for device pages |
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On Tue, Jul 14, 2020 at 12:42:11PM -0700, Dave Hansen wrote: > On 7/14/20 12:29 PM, Peter Zijlstra wrote: > > On Tue, Jul 14, 2020 at 12:06:16PM -0700, Ira Weiny wrote: > >> On Tue, Jul 14, 2020 at 10:44:51AM +0200, Peter Zijlstra wrote: > >>> So, if I followed along correctly, you're proposing to do a WRMSR per > >>> k{,un}map{_atomic}(), sounds like excellent performance all-round :-( > >> Only to pages which have this additional protection, ie not DRAM. > >> > >> User mappings of this memory is not affected (would be covered by User PKeys if > >> desired). User mappings to persistent memory are the primary use case and the > >> performant path. > > Because performance to non-volatile memory doesn't matter? I think Dave > > has a better answer here ... > > So, these WRMSRs are less evil than normal. They're architecturally > non-serializing instructions,
Excellent, that should make these a fair bit faster than regular MSRs.
> But, either way, this *will* make accessing PMEM more expensive from the > kernel. No escaping that.
There's no free lunch, it's just that regular MSRs are fairly horrible.
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