Re: make PROT_WRITE imply PROT_READ

[Arjan van de Ven <arjan@infradead.org>]

On Fri, 2006-06-23 at 10:05 -0400, Jason Baron wrote:
> On Fri, 23 Jun 2006, Arjan van de Ven wrote:
> 
> > 
> > > 
> > > hi,
> > > 
> > > So if i create a PROT_WRITE only mapping and then read from first and then 
> > > writte to it a get a SEGV. However, if i write to it first and then read 
> > > from it, i don't get a SEGV...Why should the read/write ordering matter? 
> > 
> > it matters only on those cpus that don't have explicit/separate read
> > permissions (just like PROT_EXEC is implied on cpus that don't have a
> > special permission bit for that)...
> > 
> > 
> > 
> 
> i understand that, but i'd like to see it changed so that i don't get a 
> SEGV when i read first on those cpus. ?

why? You asked for this you get it in all cases we can deliver what you
asked...

> The current behavior, besides being 
> inconsistent, is rather confusing...in addition, if ptes are copied 
> instead of faulted i get yet another type of behavior...

same for prefault I suppose, but still.

you ask for it, and the kernel is supposed to deliver the best behavior
it can.