On Tue, Dec 14, 2021 at 05:28:09PM +0000, Oliver Upton wrote:
> Allow writes to OSLAR and forward the OSLK bit to OSLSR. Do nothing with
> the value for now.
>
> Reviewed-by: Reiji Watanabe <rei...@google.com>
> Signed-off-by: Oliver Upton <oup...@google.com>
> ---
> arch/arm64/include/asm/sysreg.h | 9 ++++++++
> arch/arm64/kvm/sys_regs.c | 39 ++++++++++++++++++++++++++-------
> 2 files changed, 40 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 16b3f1a1d468..46f800bda045 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -129,7 +129,16 @@
> #define SYS_DBGWCRn_EL1(n) sys_reg(2, 0, 0, n, 7)
> #define SYS_MDRAR_EL1 sys_reg(2, 0, 1, 0, 0)
> #define SYS_OSLAR_EL1 sys_reg(2, 0, 1, 0, 4)
> +
> +#define SYS_OSLAR_OSLK BIT(0)
> +
> #define SYS_OSLSR_EL1 sys_reg(2, 0, 1, 1, 4)
> +
> +#define SYS_OSLSR_OSLK BIT(1)
> +
> +#define SYS_OSLSR_OSLM_MASK (BIT(3) | BIT(0))
> +#define SYS_OSLSR_OSLM BIT(3)
Since `OSLM` is the field as a whole, I think this should have another level of
hierarchy, e.g.
#define SYS_OSLSR_OSLM_MASK (BIT(3) | BIT(0))
#define SYS_OSLSR_OSLM_NI 0
#define SYS_OSLSR_OSLM_OSLK BIT(3)
[...]
> +static bool trap_oslar_el1(struct kvm_vcpu *vcpu,
> + struct sys_reg_params *p,
> + const struct sys_reg_desc *r)
> +{
> + u64 oslsr;
> +
> + if (!p->is_write)
> + return read_from_write_only(vcpu, p, r);
> +
> + /* Forward the OSLK bit to OSLSR */
> + oslsr = __vcpu_sys_reg(vcpu, OSLSR_EL1) & ~SYS_OSLSR_OSLK;
> + if (p->regval & SYS_OSLAR_OSLK)
> + oslsr |= SYS_OSLSR_OSLK;
> +
> + __vcpu_sys_reg(vcpu, OSLSR_EL1) = oslsr;
> + return true;
> +}
Does changing this affect existing userspace? Previosuly it could read
OSLAR_EL1 as 0, whereas now that should be rejected.
That might be fine, and if so, it would be good to call that out in the commit
message.
[...]
> @@ -309,9 +331,14 @@ static int set_oslsr_el1(struct kvm_vcpu *vcpu, const
> struct sys_reg_desc *rd,
> if (err)
> return err;
>
> - if (val != rd->val)
> + /*
> + * The only modifiable bit is the OSLK bit. Refuse the write if
> + * userspace attempts to change any other bit in the register.
> + */
> + if ((val & ~SYS_OSLSR_OSLK) != SYS_OSLSR_OSLM)
> return -EINVAL;
How about:
if ((val ^ rd->val) & ~SYS_OSLSR_OSLK)
return -EINVAL;
... so that we don't need to hard-code the expected value here, and can more
easily change it in future?
[...]
> @@ -1463,8 +1486,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
> DBG_BCR_BVR_WCR_WVR_EL1(15),
>
> { SYS_DESC(SYS_MDRAR_EL1), trap_raz_wi },
> - { SYS_DESC(SYS_OSLAR_EL1), trap_raz_wi },
> - { SYS_DESC(SYS_OSLSR_EL1), trap_oslsr_el1, reset_val, OSLSR_EL1,
> 0x00000008,
> + { SYS_DESC(SYS_OSLAR_EL1), trap_oslar_el1 },
> + { SYS_DESC(SYS_OSLSR_EL1), trap_oslsr_el1, reset_val, OSLSR_EL1,
> SYS_OSLSR_OSLM,
> .set_user = set_oslsr_el1, },
> { SYS_DESC(SYS_OSDLR_EL1), trap_raz_wi },
> { SYS_DESC(SYS_DBGPRCR_EL1), trap_raz_wi },
> @@ -1937,7 +1960,7 @@ static const struct sys_reg_desc cp14_regs[] = {
>
> DBGBXVR(0),
> /* DBGOSLAR */
> - { Op1( 0), CRn( 1), CRm( 0), Op2( 4), trap_raz_wi },
> + { Op1( 0), CRn( 1), CRm( 0), Op2( 4), trap_oslar_el1 },
As above, I have a slight concern that this could adversely affect existing
userspace, but I can also believe that's fine.
Thanks,
Mark.
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