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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Mar 01, 2019 at 01:03:36PM +0000, Julien Thierry wrote: > > > On 26/02/2019 12:13, Dave Martin wrote: > > On Thu, Feb 21, 2019 at 03:23:37PM +0000, Julien Thierry wrote: > >> Hi Dave, > >> > >> On 18/02/2019 19:52, Dave Martin wrote: > >>> This patch adds the following registers for access via the > >>> KVM_{GET,SET}_ONE_REG interface: > >>> > >>> * KVM_REG_ARM64_SVE_ZREG(n, i) (n = 0..31) (in 2048-bit slices) > >>> * KVM_REG_ARM64_SVE_PREG(n, i) (n = 0..15) (in 256-bit slices) > >>> * KVM_REG_ARM64_SVE_FFR(i) (in 256-bit slices) > >>> > >>> In order to adapt gracefully to future architectural extensions, > >>> the registers are logically divided up into slices as noted above: > >>> the i parameter denotes the slice index. > >>> > >>> This allows us to reserve space in the ABI for future expansion of > >>> these registers. However, as of today the architecture does not > >>> permit registers to be larger than a single slice, so no code is > >>> needed in the kernel to expose additional slices, for now. The > >>> code can be extended later as needed to expose them up to a maximum > >>> of 32 slices (as carved out in the architecture itself) if they > >>> really exist someday. > >>> > >>> The registers are only visible for vcpus that have SVE enabled. > >>> They are not enumerated by KVM_GET_REG_LIST on vcpus that do not > >>> have SVE. > >>> > >>> Accesses to the FPSIMD registers via KVM_REG_ARM_CORE is not > >>> allowed for SVE-enabled vcpus: SVE-aware userspace can use the > >>> KVM_REG_ARM64_SVE_ZREG() interface instead to access the same > >>> register state. This avoids some complex and pointless emulation > >>> in the kernel to convert between the two views of these aliased > >>> registers. > >>> > >>> Signed-off-by: Dave Martin [...] > >>> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c > >>> index f491456..8cfa889 100644 > >>> --- a/arch/arm64/kvm/guest.c > >>> +++ b/arch/arm64/kvm/guest.c [...] > >>> +struct sve_state_region { > >> > >> This sve_state_region feels a bit too generic too me. > >> > >> So far it is only used to access a single (slice of a) register at a > >> time. Is there a plan to use it for more? > > > > It's there as a way to factor out security-sensitive range computations > > that we otherwise have to do twice -- I'd rather have the (potential) > > bugs in one place. sve_state is particularly awkward because it is > > heterogeneous, with variably sized members for which no C declaration > > is avaiable (or possible). > > > > Previously it was used in four places, because I tried to emulate the > > VFP get/set functions for SVE vcpus. Now that functionality has been > > dropped I agree that this function looks like a bit like overkill. But > > I didn't come up with a good way to split it without duplicating an > > undesirable amount of fiddly logic. > > > > "sve_state" in the name comes from the naming of the kernel field(s) > > that this computes ranges on: vcpu->arch.sve_state (and thread-> > > sve_state, which we don't operate on here, but which has the same > > format). > > > > So, this struct describes a slice of "sve_state", hence the name. But > > you're right, it is only ever supposed to span a single SVE register > > within there. > > > >> Otherwise I'd suggest at least naming it something like sve_reg_region, > >> sve_reg_mem_region or sve_reg_mem_desc. > > > > It used to be called struct kreg_region. The name "sve_state_region" > > was an attempt to make it look less generic, which doesn't appear to > > have worked too well. > > > > Maybe "sve_state_reg_region" would narrow the apparent scope of this a > > little further. > > > > Thoughts? > > > > Yes, I think that the name fits better. That + the comment you suggested > would set things clear. > > > I'll take a look, and at least add a comment explaining what this > > struct is supposed to represent. > > > > Yes, that might prevent people looking into to much possibilities of its > usage. OK, both done. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel