Re: [RFC PATCH 15/16] KVM: arm64: Enumerate SVE register indices for KVM_GET_REG_LIST

Andrew Jones
2018-07-19T13:59:31Z

On Thu, Jun 21, 2018 at 03:57:39PM +0100, 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 extra IDs are added.
>
> On an SVE-enabled vcpu, the appropriate number of slide IDs are
> enumerated for each SVE register, depending on the maximum vector
> length for the vcpu.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> ---
> arch/arm64/kvm/guest.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 73 insertions(+)
>
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index 005394b..5152362 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -21,6 +21,7 @@
>
> #include <linux/errno.h>
> #include <linux/err.h>
> +#include <linux/kernel.h>
> #include <linux/kvm_host.h>
> #include <linux/module.h>
> #include <linux/uaccess.h>
> @@ -253,6 +254,73 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> return err;
> }
>
> +static void copy_reg_index_to_user(u64 __user **uind, int *total, int *cerr,
> + u64 id)
> +{
> + int err;
> +
> + if (*cerr)
> + return;
> +
> + if (uind) {
> + err = put_user(id, *uind);
> + if (err) {
> + *cerr = err;
> + return;
> + }
> + }
> +
> + ++*total;
> + if (uind)
> + ++*uind;
> +}
> +
> +static int enumerate_sve_regs(const struct kvm_vcpu *vcpu, u64 __user **uind)
> +{
> + unsigned int n, i;
> + int err = 0;
> + int total = 0;
> + unsigned int slices;
> +
> + if (!vcpu_has_sve(&vcpu->arch))
> + return 0;
> +
> + slices = DIV_ROUND_UP(vcpu->arch.sve_max_vl,
> + KVM_REG_SIZE(KVM_REG_ARM64_SVE_ZREG(0, 0)));
> +
> + for (n = 0; n < SVE_NUM_ZREGS; ++n)
> + for (i = 0; i < slices; ++i)
> + copy_reg_index_to_user(uind, &total, &err,
> + KVM_REG_ARM64_SVE_ZREG(n, i));
> +
> + for (n = 0; n < SVE_NUM_PREGS; ++n)
> + for (i = 0; i < slices; ++i)
> + copy_reg_index_to_user(uind, &total, &err,
> + KVM_REG_ARM64_SVE_PREG(n, i));
> +
> + for (i = 0; i < slices; ++i)
> + copy_reg_index_to_user(uind, &total, &err,
> + KVM_REG_ARM64_SVE_FFR(i));
> +
> + if (err)
> + return -EFAULT;
> +
> + return total;
> +}
> +
> +static unsigned long num_sve_regs(const struct kvm_vcpu *vcpu)
> +{
> + return enumerate_sve_regs(vcpu, NULL);
> +}
> +
> +static int copy_sve_reg_indices(const struct kvm_vcpu *vcpu, u64 __user **uind)
> +{
> + int err;
> +
> + err = enumerate_sve_regs(vcpu, uind);
> + return err < 0 ? err : 0;
> +}

I see the above functions were inspired by walk_sys_regs(), but, IMHO,
they're a bit overcomplicated. How about this untested approach?

diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index 56a0260ceb11..0188a8b30d46 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -130,6 +130,52 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
return err;
}

+static int enumerate_sve_regs(const struct kvm_vcpu *vcpu, u64 __user *uind)
+{
+ unsigned int slices = DIV_ROUND_UP(vcpu->arch.sve_max_vl,
+ KVM_REG_SIZE(KVM_REG_ARM64_SVE_ZREG(0, 0)));
+ unsigned int n, i;
+
+ if (!vcpu_has_sve(&vcpu->arch))
+ return 0;
+
+ for (n = 0; < SVE_NUM_ZREGS; ++n) {
+ for (i = 0; i < slices; ++i) {
+ if (put_user(KVM_REG_ARM64_SVE_ZREG(n, i), uind++))
+ return -EFAULT;
+ }
+ }
+
+ for (n = 0; < SVE_NUM_PREGS; ++n) {
+ for (i = 0; i < slices; ++i) {
+ if (put_user(KVM_REG_ARM64_SVE_PREG(n, i), uind++))
+ return -EFAULT;
+ }
+ }
+
+ for (i = 0; i < slices; ++i) {
+ if (put_user(KVM_REG_ARM64_SVE_FFR(i), uind++))
+ return -EFAULT;
+ }
+
+ return 0;
+}
+
+static unsigned long num_sve_regs(const struct kvm_vcpu *vcpu)
+{
+ unsigned int slices = DIV_ROUND_UP(vcpu->arch.sve_max_vl,
+ KVM_REG_SIZE(KVM_REG_ARM64_SVE_ZREG(0, 0)));
+
+ if (vcpu_has_sve(&vcpu->arch))
+ return (SVE_NUM_ZREGS + SVE_NUM_PREGS + 1) * slices;
+
+ return 0;
+}
+

> +
> static int sve_reg_bounds(struct reg_bounds_struct *b,
> const struct kvm_vcpu *vcpu,
> const struct kvm_one_reg *reg)
> @@ -403,6 +471,7 @@ unsigned long kvm_arm_num_regs(struct kvm_vcpu *vcpu)
> unsigned long res = 0;
>
> res += num_core_regs();
> + 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;
> @@ -427,6 +496,10 @@ int kvm_arm_copy_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
> uindices++;
> }
>
> + ret = copy_sve_reg_indices(vcpu, &uindices);
> + if (ret)
> + return ret;
> +
> ret = kvm_arm_copy_fw_reg_indices(vcpu, uindices);
> if (ret)
> return ret;
> --
> 2.1.4
>
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