On Thu, 29 Oct 2020 20:11:04 +0000,
Andrew Jones <drjones@xxxxxxxxxx> wrote:
>
> The instruction encodings of ID registers are preallocated. Until an
> encoding is assigned a purpose the register is RAZ. KVM's general ID
> register accessor functions already support both paths, RAZ or not.
> If for each ID register we can determine if it's RAZ or not, then all
> ID registers can build on the general functions. The register visibility
> function allows us to check whether a register should be completely
> hidden or not, extending it to also report when the register should
> be RAZ or not allows us to use it for ID registers as well.
>
> No functional change intended.
>
> Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx>
> ---
> arch/arm64/kvm/sys_regs.c | 19 ++++++++++++++++---
> arch/arm64/kvm/sys_regs.h | 20 ++++++++++++++++++++
> 2 files changed, 36 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index d24e66ee59b3..9f6151589460 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1171,7 +1171,9 @@ static bool access_id_reg(struct kvm_vcpu *vcpu,
> struct sys_reg_params *p,
> const struct sys_reg_desc *r)
> {
> - return __access_id_reg(vcpu, p, r, false);
> + bool raz = sysreg_raz_from_guest(vcpu, r);
> +
> + return __access_id_reg(vcpu, p, r, raz);
> }
>
> static bool access_raz_id_reg(struct kvm_vcpu *vcpu,
> @@ -1283,13 +1285,17 @@ static int __set_id_reg(const struct kvm_vcpu *vcpu,
> static int get_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
> const struct kvm_one_reg *reg, void __user *uaddr)
> {
> - return __get_id_reg(vcpu, rd, uaddr, false);
> + bool raz = sysreg_raz_from_user(vcpu, rd);
> +
> + return __get_id_reg(vcpu, rd, uaddr, raz);
> }
>
> static int set_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
> const struct kvm_one_reg *reg, void __user *uaddr)
> {
> - return __set_id_reg(vcpu, rd, uaddr, false);
> + bool raz = sysreg_raz_from_user(vcpu, rd);
> +
> + return __set_id_reg(vcpu, rd, uaddr, raz);
> }
>
> static int get_raz_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
> @@ -1375,12 +1381,19 @@ static bool access_mte_regs(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
> return false;
> }
>
> +static unsigned int id_visibility(const struct kvm_vcpu *vcpu,
> + const struct sys_reg_desc *r)
> +{
> + return 0;
> +}
> +
> /* sys_reg_desc initialiser for known cpufeature ID registers */
> #define ID_SANITISED(name) { \
> SYS_DESC(SYS_##name), \
> .access = access_id_reg, \
> .get_user = get_id_reg, \
> .set_user = set_id_reg, \
> + .visibility = id_visibility, \
> }
>
> /*
> diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h
> index 5a6fc30f5989..d5add36c130a 100644
> --- a/arch/arm64/kvm/sys_regs.h
> +++ b/arch/arm64/kvm/sys_regs.h
> @@ -61,6 +61,8 @@ struct sys_reg_desc {
>
> #define REG_HIDDEN_USER (1 << 0) /* hidden from userspace ioctls */
> #define REG_HIDDEN_GUEST (1 << 1) /* hidden from guest */
> +#define REG_RAZ_USER (1 << 2) /* RAZ from userspace ioctls */
> +#define REG_RAZ_GUEST (1 << 3) /* RAZ from guest */
>
> static __printf(2, 3)
> inline void print_sys_reg_msg(const struct sys_reg_params *p,
> @@ -129,6 +131,24 @@ static inline bool sysreg_hidden_from_user(const struct kvm_vcpu *vcpu,
> return r->visibility(vcpu, r) & REG_HIDDEN_USER;
> }
>
> +static inline bool sysreg_raz_from_guest(const struct kvm_vcpu *vcpu,
> + const struct sys_reg_desc *r)
> +{
> + if (likely(!r->visibility))
> + return false;
> +
> + return r->visibility(vcpu, r) & REG_RAZ_GUEST;
> +}
> +
> +static inline bool sysreg_raz_from_user(const struct kvm_vcpu *vcpu,
> + const struct sys_reg_desc *r)
> +{
> + if (likely(!r->visibility))
> + return false;
> +
> + return r->visibility(vcpu, r) & REG_RAZ_USER;
> +}
> +
> static inline int cmp_sys_reg(const struct sys_reg_desc *i1,
> const struct sys_reg_desc *i2)
> {
Is there actually a case for any ID register to have different
RAZ semantics between guest and userspace? I have the feeling that
we'd want them to be consistent at all times. Or did you have any
particular (and future) use case in mind?
Otherwise, looks good.
M.
--
Without deviation from the norm, progress is not possible.
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