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Date: Tue, 21 Apr 2015 09:36:20 +0100 From: "Jan Beulich" <JBeulich@...e.com> To: "Andrew Cooper" <andrew.cooper3@...rix.com> Cc: "David Vrabel" <david.vrabel@...rix.com>, <x86@...nel.org>, "Thomas Gleixner" <tglx@...utronix.de>, <lguest@...ts.ozlabs.org>, "Xen-devel" <xen-devel@...ts.xen.org>, "Boris Ostrovsky" <boris.ostrovsky@...cle.com>, "Ingo Molnar" <mingo@...hat.com>, "Rusty Russell" <rusty@...tcorp.com.au>, <linux-kernel@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com> Subject: Re: [Xen-devel] [PATCH] [RFC] x86/cpu: Fix SMAP check in PVOPS environments >>> On 20.04.15 at 19:09, <andrew.cooper3@...rix.com> wrote: > A different approach, given the dual nature of the AC flag now is to gate > setup_smap() on a kernel rpl of 0. SMAP necessarily can't be used in a > paravirtual situation where the kernel runs in cpl > 0. "Can't" isn't true here - for 64-bit PV Xen guests, which already toggle between two page table variants for kernel and user mode, it would be possible (but perhaps expensive) to mimic the needed behavior by introducing a 3rd set of page tables, containing only the kernel mappings. You may recall that I had even posted an RFC patch to tat effect about a year ago. Jan -- 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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