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Date: Mon, 16 Oct 2006 17:21:24 -0300 From: "Horst H. von Brand" <vonbrand@....utfsm.cl> To: mfbaustx <mfbaustx@...il.com> cc: linux-kernel@...r.kernel.org Subject: Re: copy_from_user / copy_to_user with no swap space mfbaustx <mfbaustx@...il.com> wrote: > I've been trying to find or derive a definitive answer to this > question for a while now but can't quite get over the hump. > > I understand when/why copy_<to|from>_user (and siblings) are required > (address validation, guaranteeing a process is paged in, etc...). The > question is: if you have no swap space (or virtual memory or > whatever), can there ever be a case in which any valid pointer to a > buffer in user-space would be incorrect as a result of another > process's PTE being present? Put another way: can a process be > partially paged? Yes. The executable (including data areas) and shared libraries are demand paged in (and ro areas could also be evicted), so they can very well be only partially in memory. In any case, relying on "this kernel will never have no swap" isn't wise... -- Dr. Horst H. von Brand User #22616 counter.li.org Departamento de Informatica Fono: +56 32 2654431 Universidad Tecnica Federico Santa Maria +56 32 2654239 Casilla 110-V, Valparaiso, Chile Fax: +56 32 2797513 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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