Re: [PATCH v7 19/27] KVM: arm64: Enumerate SVE register indices for KVM_GET_REG_LIST

Andrew Jones
2019-04-04T14:08:55Z

On Fri, Mar 29, 2019 at 01:00:44PM +0000, Dave Martin wrote:
> This patch includes the SVE register IDs in the list returned by
> KVM_GET_REG_LIST, as appropriate.
>
> On a non-SVE-enabled vcpu, no new IDs are added.
>
> On an SVE-enabled vcpu, IDs for the FPSIMD V-registers are removed
> from the list, since userspace is required to access the Z-
> registers instead in order to access the V-register content. For
> the variably-sized SVE registers, the appropriate set of slice IDs
> are enumerated, depending on the maximum vector length for the
> vcpu.
>
> As it currently stands, the SVE architecture never requires more
> than one slice to exist per register, so this patch adds no
> explicit support for enumerating multiple slices. The code can be
> extended straightforwardly to support this in the future, if
> needed.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> Reviewed-by: Julien Thierry <julien.thierry@arm.com>
> Tested-by: zhang.lei <zhang.lei@jp.fujitsu.com>
>
> ---
>
> Changes since v6:
>
> * [Julien Thierry] Add a #define to replace the magic "slices = 1",
> and add a comment explaining to maintainers what needs to happen if
> this is updated in the future.
>
> Changes since v5:
>
> (Dropped Julien Thierry's Reviewed-by due to non-trivial rebasing)
>
> * Move mis-split reword to prevent put_user()s being accidentally the
> correct size from KVM: arm64/sve: Add pseudo-register for the guest's
> vector lengths.
> ---
> arch/arm64/kvm/guest.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 63 insertions(+)
>
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 736d8cb..2aa80a5 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -222,6 +222,13 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> #define KVM_SVE_ZREG_SIZE KVM_REG_SIZE(KVM_REG_ARM64_SVE_ZREG(0, 0))
> #define KVM_SVE_PREG_SIZE KVM_REG_SIZE(KVM_REG_ARM64_SVE_PREG(0, 0))
>
> +/*
> + * number of register slices required to cover each whole SVE register on vcpu

s/number/Number/
s/on vcpu//

> + * NOTE: If you are tempted to modify this, you must also to rework

s/to rework/rework/

> + * sve_reg_to_region() to match:
> + */
> +#define vcpu_sve_slices(vcpu) 1
> +
> /* Bounds of a single SVE register slice within vcpu->arch.sve_state */
> struct sve_state_reg_region {
> unsigned int koffset; /* offset into sve_state in kernel memory */
> @@ -411,6 +418,56 @@ static int get_timer_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> return copy_to_user(uaddr, &val, KVM_REG_SIZE(reg->id)) ? -EFAULT : 0;
> }
>
> +static unsigned long num_sve_regs(const struct kvm_vcpu *vcpu)
> +{
> + /* Only the first slice ever exists, for now */

I'd move this comment up into the one above vcpu_sve_slices(),
and then nothing needs to change here when more slices come.

> + const unsigned int slices = vcpu_sve_slices(vcpu);
> +
> + if (!vcpu_has_sve(vcpu))
> + return 0;
> +
> + return slices * (SVE_NUM_PREGS + SVE_NUM_ZREGS + 1 /* FFR */);
> +}
> +
> +static int copy_sve_reg_indices(const struct kvm_vcpu *vcpu,
> + u64 __user *uindices)
> +{
> + /* Only the first slice ever exists, for now */

Same comment as above.

> + const unsigned int slices = vcpu_sve_slices(vcpu);
> + u64 reg;
> + unsigned int i, n;
> + int num_regs = 0;
> +
> + if (!vcpu_has_sve(vcpu))
> + return 0;
> +
> + for (i = 0; i < slices; i++) {
> + for (n = 0; n < SVE_NUM_ZREGS; n++) {
> + reg = KVM_REG_ARM64_SVE_ZREG(n, i);
> + if (put_user(reg, uindices++))
> + return -EFAULT;
> +
> + num_regs++;
> + }
> +
> + for (n = 0; n < SVE_NUM_PREGS; n++) {
> + reg = KVM_REG_ARM64_SVE_PREG(n, i);
> + if (put_user(reg, uindices++))
> + return -EFAULT;
> +
> + num_regs++;
> + }
> +
> + reg = KVM_REG_ARM64_SVE_FFR(i);
> + if (put_user(reg, uindices++))
> + return -EFAULT;
> +
> + num_regs++;
> + }

nit: the extra blank lines above the num_regs++'s give the code an odd
look (to me)

> +
> + return num_regs;
> +}
> +
> /**
> * kvm_arm_num_regs - how many registers do we present via KVM_GET_ONE_REG
> *
> @@ -421,6 +478,7 @@ unsigned long kvm_arm_num_regs(struct kvm_vcpu *vcpu)
> unsigned long res = 0;
>
> res += num_core_regs(vcpu);
> + res += num_sve_regs(vcpu);
> res += kvm_arm_num_sys_reg_descs(vcpu);
> res += kvm_arm_get_fw_num_regs(vcpu);
> res += NUM_TIMER_REGS;
> @@ -442,6 +500,11 @@ int kvm_arm_copy_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
> return ret;
> uindices += ret;
>
> + ret = copy_sve_reg_indices(vcpu, uindices);
> + if (ret)
> + return ret;
> + uindices += ret;

I know this if ret vs. if ret < 0 is being addressed already.

> +
> ret = kvm_arm_copy_fw_reg_indices(vcpu, uindices);
> if (ret)
> return ret;
> --
> 2.1.4
>

Thanks,
drew