| Message ID | 20210927124911.191729-3-alexandru.elisei@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: arm64: Minor improvements to RAZ register handling | expand |
On Mon, Sep 27, 2021 at 01:49:11PM +0100, Alexandru Elisei wrote: > PMSWINC_EL0 is a write-only register and was initially part of the VCPU > register state, but was later removed in commit 7a3ba3095a32 ("KVM: > arm64: Remove PMSWINC_EL0 shadow register"). To prevent regressions, the > register was kept accessible from userspace as Read-As-Zero (RAZ). > > The read function that is used to handle userspace reads of this > register is get_raz_id_reg(), which, while technically correct, as it > returns 0, it is not semantically correct, as PMSWINC_EL0 is not an ID > register as the function name suggests. > > Add a new function, get_raz_reg(), to use it as the accessor for > PMSWINC_EL0, as to not conflate get_raz_id_reg() to handle other types > of registers. > > No functional change intended. > > Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> > --- > arch/arm64/kvm/sys_regs.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > index 4adda8bf3168..1be827740f87 100644 > --- a/arch/arm64/kvm/sys_regs.c > +++ b/arch/arm64/kvm/sys_regs.c > @@ -1285,6 +1285,15 @@ static int set_raz_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > return __set_id_reg(vcpu, rd, uaddr, true); > } > > +static int get_raz_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > + const struct kvm_one_reg *reg, void __user *uaddr) > +{ > + const u64 id = sys_reg_to_index(rd); > + const u64 val = 0; > + > + return reg_to_user(uaddr, &val, id); > +} > + > static int set_wi_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > const struct kvm_one_reg *reg, void __user *uaddr) > { > @@ -1647,7 +1656,7 @@ static const struct sys_reg_desc sys_reg_descs[] = { > * previously (and pointlessly) advertised in the past... > */ > { PMU_SYS_REG(SYS_PMSWINC_EL0), > - .get_user = get_raz_id_reg, .set_user = set_wi_reg, > + .get_user = get_raz_reg, .set_user = set_wi_reg, > .access = access_pmswinc, .reset = NULL }, > { PMU_SYS_REG(SYS_PMSELR_EL0), > .access = access_pmselr, .reset = reset_pmselr, .reg = PMSELR_EL0 }, > -- > 2.33.0 > What about replacing get_raz_id_reg() with this new function? Do really need both? Thanks, drew
Hi Drew, Thank you for the review! On Thu, Sep 30, 2021 at 03:29:15PM +0200, Andrew Jones wrote: > On Mon, Sep 27, 2021 at 01:49:11PM +0100, Alexandru Elisei wrote: > > PMSWINC_EL0 is a write-only register and was initially part of the VCPU > > register state, but was later removed in commit 7a3ba3095a32 ("KVM: > > arm64: Remove PMSWINC_EL0 shadow register"). To prevent regressions, the > > register was kept accessible from userspace as Read-As-Zero (RAZ). > > > > The read function that is used to handle userspace reads of this > > register is get_raz_id_reg(), which, while technically correct, as it > > returns 0, it is not semantically correct, as PMSWINC_EL0 is not an ID > > register as the function name suggests. > > > > Add a new function, get_raz_reg(), to use it as the accessor for > > PMSWINC_EL0, as to not conflate get_raz_id_reg() to handle other types > > of registers. > > > > No functional change intended. > > > > Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> > > --- > > arch/arm64/kvm/sys_regs.c | 11 ++++++++++- > > 1 file changed, 10 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > > index 4adda8bf3168..1be827740f87 100644 > > --- a/arch/arm64/kvm/sys_regs.c > > +++ b/arch/arm64/kvm/sys_regs.c > > @@ -1285,6 +1285,15 @@ static int set_raz_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > > return __set_id_reg(vcpu, rd, uaddr, true); > > } > > > > +static int get_raz_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > > + const struct kvm_one_reg *reg, void __user *uaddr) > > +{ > > + const u64 id = sys_reg_to_index(rd); > > + const u64 val = 0; > > + > > + return reg_to_user(uaddr, &val, id); > > +} > > + > > static int set_wi_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > > const struct kvm_one_reg *reg, void __user *uaddr) > > { > > @@ -1647,7 +1656,7 @@ static const struct sys_reg_desc sys_reg_descs[] = { > > * previously (and pointlessly) advertised in the past... > > */ > > { PMU_SYS_REG(SYS_PMSWINC_EL0), > > - .get_user = get_raz_id_reg, .set_user = set_wi_reg, > > + .get_user = get_raz_reg, .set_user = set_wi_reg, > > .access = access_pmswinc, .reset = NULL }, > > { PMU_SYS_REG(SYS_PMSELR_EL0), > > .access = access_pmselr, .reset = reset_pmselr, .reg = PMSELR_EL0 }, > > -- > > 2.33.0 > > > > What about replacing get_raz_id_reg() with this new function? Do really need > both? I thought about that when writing this patch. I ultimately decided against it because changing the get_user accessor to be get_raz_reg() instead of get_raz_id_reg() would break the symmetry with set_user, which needs to stay set_raz_id_reg(), and cannot be substituted with set_wi_reg() because that would be a change in behaviour (set_raz_id_reg() checks that val == 0, set_wi_reg() doesn't). I do agree that get_raz_id_reg() does the exact same thing as get_raz_reg(), but in a more roundabout manner. So if you still feel that I should use get_raz_reg() instead, I'll do that for the next iteration of the series. What do you think? Thanks, Alex > > Thanks, > drew >
On Wed, Oct 06, 2021 at 03:49:19PM +0100, Alexandru Elisei wrote: > Hi Drew, > > Thank you for the review! > > On Thu, Sep 30, 2021 at 03:29:15PM +0200, Andrew Jones wrote: > > On Mon, Sep 27, 2021 at 01:49:11PM +0100, Alexandru Elisei wrote: > > > PMSWINC_EL0 is a write-only register and was initially part of the VCPU > > > register state, but was later removed in commit 7a3ba3095a32 ("KVM: > > > arm64: Remove PMSWINC_EL0 shadow register"). To prevent regressions, the > > > register was kept accessible from userspace as Read-As-Zero (RAZ). > > > > > > The read function that is used to handle userspace reads of this > > > register is get_raz_id_reg(), which, while technically correct, as it > > > returns 0, it is not semantically correct, as PMSWINC_EL0 is not an ID > > > register as the function name suggests. > > > > > > Add a new function, get_raz_reg(), to use it as the accessor for > > > PMSWINC_EL0, as to not conflate get_raz_id_reg() to handle other types > > > of registers. > > > > > > No functional change intended. > > > > > > Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> > > > --- > > > arch/arm64/kvm/sys_regs.c | 11 ++++++++++- > > > 1 file changed, 10 insertions(+), 1 deletion(-) > > > > > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > > > index 4adda8bf3168..1be827740f87 100644 > > > --- a/arch/arm64/kvm/sys_regs.c > > > +++ b/arch/arm64/kvm/sys_regs.c > > > @@ -1285,6 +1285,15 @@ static int set_raz_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > > > return __set_id_reg(vcpu, rd, uaddr, true); > > > } > > > > > > +static int get_raz_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > > > + const struct kvm_one_reg *reg, void __user *uaddr) > > > +{ > > > + const u64 id = sys_reg_to_index(rd); > > > + const u64 val = 0; > > > + > > > + return reg_to_user(uaddr, &val, id); > > > +} > > > + > > > static int set_wi_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > > > const struct kvm_one_reg *reg, void __user *uaddr) > > > { > > > @@ -1647,7 +1656,7 @@ static const struct sys_reg_desc sys_reg_descs[] = { > > > * previously (and pointlessly) advertised in the past... > > > */ > > > { PMU_SYS_REG(SYS_PMSWINC_EL0), > > > - .get_user = get_raz_id_reg, .set_user = set_wi_reg, > > > + .get_user = get_raz_reg, .set_user = set_wi_reg, > > > .access = access_pmswinc, .reset = NULL }, > > > { PMU_SYS_REG(SYS_PMSELR_EL0), > > > .access = access_pmselr, .reset = reset_pmselr, .reg = PMSELR_EL0 }, > > > -- > > > 2.33.0 > > > > > > > What about replacing get_raz_id_reg() with this new function? Do really need > > both? > > I thought about that when writing this patch. I ultimately decided against it > because changing the get_user accessor to be get_raz_reg() instead of > get_raz_id_reg() would break the symmetry with set_user, which needs to stay > set_raz_id_reg(), and cannot be substituted with set_wi_reg() because that would > be a change in behaviour (set_raz_id_reg() checks that val == 0, set_wi_reg() > doesn't). > > I do agree that get_raz_id_reg() does the exact same thing as get_raz_reg(), but > in a more roundabout manner. So if you still feel that I should use > get_raz_reg() instead, I'll do that for the next iteration of the series. What > do you think? I'd prefer we avoid maintaining two implementations of the same functionality. If we want to keep the symmetry with set_raz_id_reg, then we could implement get_raz_id_reg as 'return get_raz_reg()'. Thanks, drew
Hi Drew, On Wed, Oct 06, 2021 at 05:23:02PM +0200, Andrew Jones wrote: > On Wed, Oct 06, 2021 at 03:49:19PM +0100, Alexandru Elisei wrote: > > Hi Drew, > > > > Thank you for the review! > > > > On Thu, Sep 30, 2021 at 03:29:15PM +0200, Andrew Jones wrote: > > > On Mon, Sep 27, 2021 at 01:49:11PM +0100, Alexandru Elisei wrote: > > > > PMSWINC_EL0 is a write-only register and was initially part of the VCPU > > > > register state, but was later removed in commit 7a3ba3095a32 ("KVM: > > > > arm64: Remove PMSWINC_EL0 shadow register"). To prevent regressions, the > > > > register was kept accessible from userspace as Read-As-Zero (RAZ). > > > > > > > > The read function that is used to handle userspace reads of this > > > > register is get_raz_id_reg(), which, while technically correct, as it > > > > returns 0, it is not semantically correct, as PMSWINC_EL0 is not an ID > > > > register as the function name suggests. > > > > > > > > Add a new function, get_raz_reg(), to use it as the accessor for > > > > PMSWINC_EL0, as to not conflate get_raz_id_reg() to handle other types > > > > of registers. > > > > > > > > No functional change intended. > > > > > > > > Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> > > > > --- > > > > arch/arm64/kvm/sys_regs.c | 11 ++++++++++- > > > > 1 file changed, 10 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > > > > index 4adda8bf3168..1be827740f87 100644 > > > > --- a/arch/arm64/kvm/sys_regs.c > > > > +++ b/arch/arm64/kvm/sys_regs.c > > > > @@ -1285,6 +1285,15 @@ static int set_raz_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > > > > return __set_id_reg(vcpu, rd, uaddr, true); > > > > } > > > > > > > > +static int get_raz_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > > > > + const struct kvm_one_reg *reg, void __user *uaddr) > > > > +{ > > > > + const u64 id = sys_reg_to_index(rd); > > > > + const u64 val = 0; > > > > + > > > > + return reg_to_user(uaddr, &val, id); > > > > +} > > > > + > > > > static int set_wi_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, > > > > const struct kvm_one_reg *reg, void __user *uaddr) > > > > { > > > > @@ -1647,7 +1656,7 @@ static const struct sys_reg_desc sys_reg_descs[] = { > > > > * previously (and pointlessly) advertised in the past... > > > > */ > > > > { PMU_SYS_REG(SYS_PMSWINC_EL0), > > > > - .get_user = get_raz_id_reg, .set_user = set_wi_reg, > > > > + .get_user = get_raz_reg, .set_user = set_wi_reg, > > > > .access = access_pmswinc, .reset = NULL }, > > > > { PMU_SYS_REG(SYS_PMSELR_EL0), > > > > .access = access_pmselr, .reset = reset_pmselr, .reg = PMSELR_EL0 }, > > > > -- > > > > 2.33.0 > > > > > > > > > > What about replacing get_raz_id_reg() with this new function? Do really need > > > both? > > > > I thought about that when writing this patch. I ultimately decided against it > > because changing the get_user accessor to be get_raz_reg() instead of > > get_raz_id_reg() would break the symmetry with set_user, which needs to stay > > set_raz_id_reg(), and cannot be substituted with set_wi_reg() because that would > > be a change in behaviour (set_raz_id_reg() checks that val == 0, set_wi_reg() > > doesn't). > > > > I do agree that get_raz_id_reg() does the exact same thing as get_raz_reg(), but > > in a more roundabout manner. So if you still feel that I should use > > get_raz_reg() instead, I'll do that for the next iteration of the series. What > > do you think? > > I'd prefer we avoid maintaining two implementations of the same > functionality. If we want to keep the symmetry with set_raz_id_reg, > then we could implement get_raz_id_reg as 'return get_raz_reg()'. Agreed, I'll replace get_raz_id_reg() with get_raz_reg(). Thanks, Alex > > Thanks, > drew >
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index 4adda8bf3168..1be827740f87 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -1285,6 +1285,15 @@ static int set_raz_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, return __set_id_reg(vcpu, rd, uaddr, true); } +static int get_raz_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, + const struct kvm_one_reg *reg, void __user *uaddr) +{ + const u64 id = sys_reg_to_index(rd); + const u64 val = 0; + + return reg_to_user(uaddr, &val, id); +} + static int set_wi_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd, const struct kvm_one_reg *reg, void __user *uaddr) { @@ -1647,7 +1656,7 @@ static const struct sys_reg_desc sys_reg_descs[] = { * previously (and pointlessly) advertised in the past... */ { PMU_SYS_REG(SYS_PMSWINC_EL0), - .get_user = get_raz_id_reg, .set_user = set_wi_reg, + .get_user = get_raz_reg, .set_user = set_wi_reg, .access = access_pmswinc, .reset = NULL }, { PMU_SYS_REG(SYS_PMSELR_EL0), .access = access_pmselr, .reset = reset_pmselr, .reg = PMSELR_EL0 },
PMSWINC_EL0 is a write-only register and was initially part of the VCPU register state, but was later removed in commit 7a3ba3095a32 ("KVM: arm64: Remove PMSWINC_EL0 shadow register"). To prevent regressions, the register was kept accessible from userspace as Read-As-Zero (RAZ). The read function that is used to handle userspace reads of this register is get_raz_id_reg(), which, while technically correct, as it returns 0, it is not semantically correct, as PMSWINC_EL0 is not an ID register as the function name suggests. Add a new function, get_raz_reg(), to use it as the accessor for PMSWINC_EL0, as to not conflate get_raz_id_reg() to handle other types of registers. No functional change intended. Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> --- arch/arm64/kvm/sys_regs.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)