On Tue, Nov 03, 2020 at 11:23:54AM +0000, Dave Martin wrote:
> On Mon, Nov 02, 2020 at 07:50:36PM +0100, Andrew Jones 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.
>
> Nit: no statement of what the patch does.
Hmm, I'm not sure what "...extending it to also report when the register
should be RAZ or not allows us to use it for ID registers as well." is
missing, other than spelling out that a new flag is being added for the
extension. Please provide a suggestion.
>
> You might want to point out that the introduced REG_RAZ functionality is
> intentionally not used in this patch.
OK
>
> > No functional change intended.
> >
> > Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx>
> > ---
> > arch/arm64/kvm/sys_regs.c | 19 ++++++++++++++++---
> > arch/arm64/kvm/sys_regs.h | 10 ++++++++++
> > 2 files changed, 26 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> > index 6ff0c15531ca..b8822a20b1ea 100644
> > --- a/arch/arm64/kvm/sys_regs.c
> > +++ b/arch/arm64/kvm/sys_regs.c
> > @@ -1153,6 +1153,12 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
> > return val;
> > }
> >
> > +static unsigned int id_visibility(const struct kvm_vcpu *vcpu,
> > + const struct sys_reg_desc *r)
> > +{
> > + return 0;
> > +}
> > +
> > /* cpufeature ID register access trap handlers */
> >
> > static bool __access_id_reg(struct kvm_vcpu *vcpu,
> > @@ -1171,7 +1177,9 @@ 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_visible_as_raz(vcpu, r);
> > +
> > + return __access_id_reg(vcpu, p, r, raz);
> > }
> >
> > static bool access_raz_id_reg(struct kvm_vcpu *vcpu,
> > @@ -1283,13 +1291,17 @@ 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_visible_as_raz(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_visible_as_raz(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,
> > @@ -1381,6 +1393,7 @@ static bool access_mte_regs(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
> > .access = access_id_reg, \
> > .get_user = get_id_reg, \
> > .set_user = set_id_reg, \
> > + .visibility = id_visibility, \
>
> This is just the default for ID_SANITISED, right?
The default was not to have a visibility function. Now it has one. It
still behaves the same way in this patch, though, because it just returns
zero.
>
> > }
> >
> > /*
> > diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h
> > index 5a6fc30f5989..9d3ef7cfa116 100644
> > --- a/arch/arm64/kvm/sys_regs.h
> > +++ b/arch/arm64/kvm/sys_regs.h
> > @@ -61,6 +61,7 @@ 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 (1 << 2) /* RAZ from userspace ioctls and guest */
> >
> > static __printf(2, 3)
> > inline void print_sys_reg_msg(const struct sys_reg_params *p,
> > @@ -129,6 +130,15 @@ static inline bool sysreg_hidden_from_user(const struct kvm_vcpu *vcpu,
> > return r->visibility(vcpu, r) & REG_HIDDEN_USER;
> > }
> >
> > +static inline bool sysreg_visible_as_raz(const struct kvm_vcpu *vcpu,
> > + const struct sys_reg_desc *r)
> > +{
> > + if (likely(!r->visibility))
> > + return false;
> > +
> > + return r->visibility(vcpu, r) & REG_RAZ;
> > +}
> > +
>
> [...]
>
> Looks reasonable, I think.
Thanks,
drew
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