Dave Martin <[email protected]> writes: > On Mon, Nov 19, 2018 at 04:48:36PM +0000, Alex Bennée wrote: >> >> Dave Martin <[email protected]> writes: >> >> > The Arm SVE architecture defines registers that are up to 2048 bits >> > in size (with some possibility of further future expansion). >> > >> > In order to avoid the need for an excessively large number of >> > ioctls when saving and restoring a vcpu's registers, this patch >> > adds a #define to make support for individual 2048-bit registers >> > through the KVM_{GET,SET}_ONE_REG ioctl interface official. This >> > will allow each SVE register to be accessed in a single call. >> > >> > There are sufficient spare bits in the register id size field for >> > this change, so there is no ABI impact providing that >> > KVM_GET_REG_LIST does not enumerate any 2048-bit register unless >> > userspace explicitly opts in to the relevant architecture-specific >> > features. >> > >> > Signed-off-by: Dave Martin <[email protected]> >> > --- >> > include/uapi/linux/kvm.h | 1 + >> > 1 file changed, 1 insertion(+) >> > >> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >> > index 251be35..7c3c5cc 100644 >> > --- a/include/uapi/linux/kvm.h >> > +++ b/include/uapi/linux/kvm.h >> > @@ -1110,6 +1110,7 @@ struct kvm_dirty_tlb { >> > #define KVM_REG_SIZE_U256 0x0050000000000000ULL >> > #define KVM_REG_SIZE_U512 0x0060000000000000ULL >> > #define KVM_REG_SIZE_U1024 0x0070000000000000ULL >> > +#define KVM_REG_SIZE_U2048 0x0080000000000000ULL >> >> Yeah OK I guess - but it does make me question if KVM_REG_SIZE_MASK is >> part of the ABI because although we have space for another few bits that >> is the last one without changing the mask. > > Debatable, but KVM_REG_SIZE_MASK is UAPI and suggests a clear intent not > to recycle bit 55 for another purpose. This allows for reg sizes up to > 262144 bits which is hopefully more than enough for the foreseeable > future. > > Even if bits 56-59 are currently always 0, KVM_REG_ARCH_MASK suggests > that these bits aren't going to be used for size field bits. > > > Or am I missing something?
No you are quite right - I thought I was watching an incrementing bit position not an incrementing number. Too much staring at defines, carry on ;-) > >> Reviewed-by: Alex Bennée <[email protected]> > > Thanks > ---Dave -- Alex Bennée _______________________________________________ kvmarm mailing list [email protected] https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
