Re: [PATCH v2 2/5] KVM: arm64: Get rid of host SVE tracking/saving

Mark Brown
2021-11-23T12:33:26Z

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On Tue, Nov 23, 2021 at 10:11:33AM +0000, Marc Zyngier wrote:
> Mark Brown <broonie@kernel.org> wrote:

> > We don't need to change the ABI, the ABI just says we zero the registers
> > that aren't shared with FPSIMD. Instead of doing that on taking a SVE
> > access trap to reenable SVE after having disabled TIF_SVE we could do

> That's not the point I'm trying to make.

> Userspace expects to have lost SVE information over a syscall (even if
> the VL is 128, it expects to have lost P0..P15 and FFR). How do you
> plan to tell userspace that this behaviour has changed?

My point is that this doesn't need to change. Userspace can't tell if
we zeroed the non-shared state on syscall or on some later access trap.

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