Re: [RFC PATCH] x86 NMI-safe INT3 and Page Fault (v5)

[H. Peter Anvin]

Mathieu Desnoyers wrote:
> * H. Peter Anvin (hpa@xxxxxxxxx) wrote:
> > Pavel Machek wrote:
> > > > There is also the page fault case. I think putting this test in
> > > > ret_from_exception would be both safe (it is executed for any
> > > > exception return) and fast (exceptions are rare).
> > > Eh? I thought that page fault is one of the hottest paths in kernel
> > > (along with syscall and packet receive/send)...
> > > 								Pavel
>
> On x86_64, we can pinpoint only the page faults returning to the kernel,
> which are rare and only caused by vmalloc accesses. Ideally we could do
> the same on x86_32.

Pinpoint, how?  Ultimately you need a runtime test, and you better be 
showing that people are going to die unless before you add a cycle to 
the page fault path.  I'm only slightly exaggerating that.

	-hpa

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