| Message ID | 1538141967-15375-11-git-send-email-Dave.Martin@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: arm64: Initial support for SVE guests | expand |
On Fri, Sep 28, 2018 at 02:39:14PM +0100, Dave Martin wrote: > The reset_unknown() system register helper initialises a guest > register to a distinctive junk value on vcpu reset, to help expose > and debug deficient register initialisation within the guest. > > Some registers such as the SVE control register ZCR_EL1 contain a > mixture of UNKNOWN fields and RES0 bits. For these, > reset_unknown() does not work at present, since it sets all bits to > junk values instead of just the wanted bits. > > There is no need to craft another special helper just for that, > since reset_unknown() almost does the appropriate thing anyway. > This patch takes advantage of the ununused val field in struct > sys_reg_desc to specify a mask of bits that should be initialised > to zero instead of junk. > > All existing users of reset_unknown() do not (and should not) > define a value for val, so they will implicitly set it to zero, > resulting in all bits being made UNKNOWN by this function: thus, > this patch makes no functional change for currently defined > registers. > > Future patches will make use of non-zero val. > > Signed-off-by: Dave Martin <Dave.Martin@arm.com> > --- > arch/arm64/kvm/sys_regs.h | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h > index cd710f8..24bac06 100644 > --- a/arch/arm64/kvm/sys_regs.h > +++ b/arch/arm64/kvm/sys_regs.h > @@ -89,7 +89,9 @@ static inline void reset_unknown(struct kvm_vcpu *vcpu, > { > BUG_ON(!r->reg); > BUG_ON(r->reg >= NR_SYS_REGS); > - __vcpu_sys_reg(vcpu, r->reg) = 0x1de7ec7edbadc0deULL; > + > + /* If non-zero, r->val specifies which register bits are RES0: */ > + __vcpu_sys_reg(vcpu, r->reg) = 0x1de7ec7edbadc0deULL & ~r->val; nit: it would be nice to document this feature on the val field in the sys_reg_desc structure above as well. > } > > static inline void reset_val(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r) > -- > 2.1.4 > Thanks, Christoffer
On Fri, Nov 02, 2018 at 09:11:19AM +0100, Christoffer Dall wrote: > On Fri, Sep 28, 2018 at 02:39:14PM +0100, Dave Martin wrote: > > The reset_unknown() system register helper initialises a guest > > register to a distinctive junk value on vcpu reset, to help expose > > and debug deficient register initialisation within the guest. > > > > Some registers such as the SVE control register ZCR_EL1 contain a > > mixture of UNKNOWN fields and RES0 bits. For these, > > reset_unknown() does not work at present, since it sets all bits to > > junk values instead of just the wanted bits. > > > > There is no need to craft another special helper just for that, > > since reset_unknown() almost does the appropriate thing anyway. > > This patch takes advantage of the ununused val field in struct > > sys_reg_desc to specify a mask of bits that should be initialised > > to zero instead of junk. > > > > All existing users of reset_unknown() do not (and should not) > > define a value for val, so they will implicitly set it to zero, > > resulting in all bits being made UNKNOWN by this function: thus, > > this patch makes no functional change for currently defined > > registers. > > > > Future patches will make use of non-zero val. > > > > Signed-off-by: Dave Martin <Dave.Martin@arm.com> > > --- > > arch/arm64/kvm/sys_regs.h | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h > > index cd710f8..24bac06 100644 > > --- a/arch/arm64/kvm/sys_regs.h > > +++ b/arch/arm64/kvm/sys_regs.h > > @@ -89,7 +89,9 @@ static inline void reset_unknown(struct kvm_vcpu *vcpu, > > { > > BUG_ON(!r->reg); > > BUG_ON(r->reg >= NR_SYS_REGS); > > - __vcpu_sys_reg(vcpu, r->reg) = 0x1de7ec7edbadc0deULL; > > + > > + /* If non-zero, r->val specifies which register bits are RES0: */ > > + __vcpu_sys_reg(vcpu, r->reg) = 0x1de7ec7edbadc0deULL & ~r->val; > > nit: it would be nice to document this feature on the val field in the > sys_reg_desc structure above as well. Sure thing, I missed that, but we _do_ want this clearly documented. I'll add that when I respin. [...] Cheers ---Dave
diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h index cd710f8..24bac06 100644 --- a/arch/arm64/kvm/sys_regs.h +++ b/arch/arm64/kvm/sys_regs.h @@ -89,7 +89,9 @@ static inline void reset_unknown(struct kvm_vcpu *vcpu, { BUG_ON(!r->reg); BUG_ON(r->reg >= NR_SYS_REGS); - __vcpu_sys_reg(vcpu, r->reg) = 0x1de7ec7edbadc0deULL; + + /* If non-zero, r->val specifies which register bits are RES0: */ + __vcpu_sys_reg(vcpu, r->reg) = 0x1de7ec7edbadc0deULL & ~r->val; } static inline void reset_val(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
The reset_unknown() system register helper initialises a guest register to a distinctive junk value on vcpu reset, to help expose and debug deficient register initialisation within the guest. Some registers such as the SVE control register ZCR_EL1 contain a mixture of UNKNOWN fields and RES0 bits. For these, reset_unknown() does not work at present, since it sets all bits to junk values instead of just the wanted bits. There is no need to craft another special helper just for that, since reset_unknown() almost does the appropriate thing anyway. This patch takes advantage of the ununused val field in struct sys_reg_desc to specify a mask of bits that should be initialised to zero instead of junk. All existing users of reset_unknown() do not (and should not) define a value for val, so they will implicitly set it to zero, resulting in all bits being made UNKNOWN by this function: thus, this patch makes no functional change for currently defined registers. Future patches will make use of non-zero val. Signed-off-by: Dave Martin <Dave.Martin@arm.com> --- arch/arm64/kvm/sys_regs.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)