Date: Tue, 1 Aug 2017 15:32:27 +0100 From: Will Deacon <will.deacon@....com> To: Mark Rutland <mark.rutland@....com> Cc: Christoffer Dall <cdall@...aro.org>, linux-arm-kernel@...ts.infradead.org, arnd@...db.de, catalin.marinas@....com, christoffer.dall@...aro.org, Dave.Martin@....com, jiong.wang@....com, kvmarm@...ts.cs.columbia.edu, linux-arch@...r.kernel.org, marc.zyngier@....com, suzuki.poulose@....com, yao.qi@....com, linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com Subject: Re: [PATCH 10/11] arm64/kvm: context-switch ptrauth registers On Tue, Aug 01, 2017 at 03:26:07PM +0100, Mark Rutland wrote: > On Tue, Aug 01, 2017 at 01:00:14PM +0200, Christoffer Dall wrote: > > On Wed, Jul 19, 2017 at 05:01:31PM +0100, Mark Rutland wrote: > > > When pointer authentication is supported, a guest may wish to use it. > > > This patch adds the necessary KVM infrastructure for this to work, with > > > a semi-lazy context switch of the pointer auth state. > > > > > > When we schedule a vcpu, we disable guest usage of pointer > > > authentication instructions and accesses to the keys. While these are > > > disabled, we avoid context-switching the keys. When we trap the guest > > > trying to use pointer authentication functionality, we change to eagerly > > > context-switching the keys, and enable the feature. The next time the > > > vcpu is scheduled out/in, we start again. > > > > > > This is sufficient for systems with uniform pointer authentication > > > support. For systems with mismatched support, it will be necessary to > > > > What is mismatched support? You mean systems where one CPU has ptrauth > > and another one doesn't (or if they both have it but in different ways)? > > Both! Any case where the support is not uniform across all CPUs. > > A CPU can implement address auth and/or generic auth, and either may use > an architected algorithm or an IMP DEF algorithm. > > Even if all CPUs report an IMP DEF algorithm, the particular algorithm > may differ across CPUs. I know you don't like it, but I think we should resort to MIDR at that point because otherwise IMP DEF algorithms will never be used by Linux and people will complain. Will
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