Hi Reiji,
On 12/4/21 5:35 AM, Reiji Watanabe wrote:
> Hi Eric,
>
> On Thu, Dec 2, 2021 at 4:51 AM Eric Auger <eauger@xxxxxxxxxx> wrote:
>>
>> Hi Reiji,
>>
>> On 11/17/21 7:43 AM, Reiji Watanabe wrote:
>>> This patch lays the groundwork to make ID registers writable.
>>>
>>> Introduce struct id_reg_info for an ID register to manage the
>>> register specific control of its value for the guest, and provide set
>>> of functions commonly used for ID registers to make them writable.
>>>
>>> The id_reg_info is used to do register specific initialization,
>>> validation of the ID register and etc. Not all ID registers must
>>> have the id_reg_info. ID registers that don't have the id_reg_info
>>> are handled in a common way that is applied to all ID registers.
>>>
>>> At present, changing an ID register from userspace is allowed only
>>> if the ID register has the id_reg_info, but that will be changed
>>> by the following patches.
>>>
>>> No ID register has the structure yet and the following patches
>>> will add the id_reg_info for some ID registers.
>>>
>>> Signed-off-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
>>> ---
>>> arch/arm64/include/asm/sysreg.h | 1 +
>>> arch/arm64/kvm/sys_regs.c | 226 ++++++++++++++++++++++++++++++--
>>> 2 files changed, 218 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
>>> index 16b3f1a1d468..597609f26331 100644
>>> --- a/arch/arm64/include/asm/sysreg.h
>>> +++ b/arch/arm64/include/asm/sysreg.h
>>> @@ -1197,6 +1197,7 @@
>>> #define ICH_VTR_TDS_MASK (1 << ICH_VTR_TDS_SHIFT)
>>>
>>> #define ARM64_FEATURE_FIELD_BITS 4
>>> +#define ARM64_FEATURE_FIELD_MASK ((1ull << ARM64_FEATURE_FIELD_BITS) - 1)
>>>
>>> /* Create a mask for the feature bits of the specified feature. */
>>> #define ARM64_FEATURE_MASK(x) (GENMASK_ULL(x##_SHIFT + ARM64_FEATURE_FIELD_BITS - 1, x##_SHIFT))
>>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>>> index 5608d3410660..1552cd5581b7 100644
>>> --- a/arch/arm64/kvm/sys_regs.c
>>> +++ b/arch/arm64/kvm/sys_regs.c
>>> @@ -265,6 +265,181 @@ static bool trap_raz_wi(struct kvm_vcpu *vcpu,
>>> return read_zero(vcpu, p);
>>> }
>>>
>>> +/*
>>> + * A value for FCT_LOWER_SAFE must be zero and changing that will affect
>>> + * ftr_check_types of id_reg_info.
>>> + */
>>> +enum feature_check_type {
>>> + FCT_LOWER_SAFE = 0,
>>> + FCT_HIGHER_SAFE,
>>> + FCT_HIGHER_OR_ZERO_SAFE,
>>> + FCT_EXACT,
>>> + FCT_EXACT_OR_ZERO_SAFE,
>>> + FCT_IGNORE, /* Don't check (any value is fine) */
>>> +};
>>> +
>>> +static int arm64_check_feature_one(enum feature_check_type type, int val,
>>> + int limit)
>>> +{
>>> + bool is_safe = false;
>>> +
>>> + if (val == limit)
>>> + return 0;
>>> +
>>> + switch (type) {
>>> + case FCT_LOWER_SAFE:
>>> + is_safe = (val <= limit);
>>> + break;
>>> + case FCT_HIGHER_OR_ZERO_SAFE:
>>> + if (val == 0) {
>>> + is_safe = true;
>>> + break;
>>> + }
>>> + fallthrough;
>>> + case FCT_HIGHER_SAFE:
>>> + is_safe = (val >= limit);
>>> + break;
>>> + case FCT_EXACT:
>>> + break;
>>> + case FCT_EXACT_OR_ZERO_SAFE:
>>> + is_safe = (val == 0);
>>> + break;
>>> + case FCT_IGNORE:
>>> + is_safe = true;
>>> + break;
>>> + default:
>>> + WARN_ONCE(1, "Unexpected feature_check_type (%d)\n", type);
>>> + break;
>>> + }
>>> +
>>> + return is_safe ? 0 : -1;
>>> +}
>>> +
>>> +#define FCT_TYPE_MASK 0x7
>>> +#define FCT_TYPE_SHIFT 1
>>> +#define FCT_SIGN_MASK 0x1
>>> +#define FCT_SIGN_SHIFT 0
>>> +#define FCT_TYPE(val) ((val >> FCT_TYPE_SHIFT) & FCT_TYPE_MASK)
>>> +#define FCT_SIGN(val) ((val >> FCT_SIGN_SHIFT) & FCT_SIGN_MASK)
>>> +
>>> +#define MAKE_FCT(shift, type, sign) \
>>> + ((u64)((((type) & FCT_TYPE_MASK) << FCT_TYPE_SHIFT) | \
>>> + (((sign) & FCT_SIGN_MASK) << FCT_SIGN_SHIFT)) << (shift))
>>> +
>>> +/* For signed field */
>>> +#define S_FCT(shift, type) MAKE_FCT(shift, type, 1)
>>> +/* For unigned field */
>>> +#define U_FCT(shift, type) MAKE_FCT(shift, type, 0)
>>> +
>>> +/*
>>> + * @val and @lim are both a value of the ID register. The function checks
>>> + * if all features indicated in @val can be supported for guests on the host,
>>> + * which supports features indicated in @lim. @check_types indicates how
>>> + * features in the ID register needs to be checked.
>>> + * See comments for id_reg_info's ftr_check_types field for more detail.
>>> + */
>>> +static int arm64_check_features(u64 check_types, u64 val, u64 lim)
>>> +{
>>> + int i;
>>> +
>>> + for (i = 0; i < 64; i += ARM64_FEATURE_FIELD_BITS) {
>>> + u8 ftr_check = (check_types >> i) & ARM64_FEATURE_FIELD_MASK;
>>> + bool is_sign = FCT_SIGN(ftr_check);
>>> + enum feature_check_type fctype = FCT_TYPE(ftr_check);
>>> + int fval, flim, ret;
>>> +
>>> + fval = cpuid_feature_extract_field(val, i, is_sign);
>>> + flim = cpuid_feature_extract_field(lim, i, is_sign);
>>> +
>>> + ret = arm64_check_feature_one(fctype, fval, flim);
>>> + if (ret)
>>> + return -E2BIG;
>>> + }
>>> + return 0;
>>> +}
>>> +
>>> +struct id_reg_info {
>>> + u32 sys_reg; /* Register ID */
>>> +
>>> + /*
>>> + * Limit value of the register for a vcpu. The value is the sanitized
>>> + * system value with bits cleared for unsupported features for the
>>> + * guest.
>>> + */
>>> + u64 vcpu_limit_val;
>>> +
>>> + /*
>>> + * The ftr_check_types is comprised of a set of 4 bits fields.
>>> + * Each 4 bits field is for a feature indicated by the same bits
>>> + * field of the ID register and indicates how the feature support
>>> + * for guests needs to be checked.
>>> + * The bit 0 indicates that the corresponding ID register field
>>> + * is signed(1) or unsigned(0).
>>> + * The bits [3:1] hold feature_check_type for the field.
>>> + * If all zero, all features in the ID register are treated as unsigned
>>> + * fields and checked based on Principles of the ID scheme for fields
>>> + * in ID registers (FCT_LOWER_SAFE of feature_check_type).
>>> + */
>>> + u64 ftr_check_types;
>>> +
>>> + /* Initialization function of the id_reg_info */
>>> + void (*init)(struct id_reg_info *id_reg);
>>> +
>>> + /* Register specific validation function */
>>> + int (*validate)(struct kvm_vcpu *vcpu, const struct id_reg_info *id_reg,
>>> + u64 val);
>>> +
>>> + /* Return the reset value of the register for the vCPU */
>>> + u64 (*get_reset_val)(struct kvm_vcpu *vcpu,
>>> + const struct id_reg_info *id_reg);
>> It is unclear to me why we need 2 different callbacks, ie. init and
>> get_reset_val. ID_REGS can only be accessed from user space after the
>> vcpu reset, right? So couldn't we have a single cb instead of this
>> overwrite mechanism?
>
> Thank you for the comment.
>
> What the init() does needs to be done just once.
> It initializes the id_reg_info itself (not for the ID register of vCPU).
> And the data initialized by the init() is used not just for the
> overwrite mechanism at the vcpu reset but for other purposes as well.
>
> What the get_reset_val does needs to be done for every initial vCPU reset.
> It provides the initial value for the vCPU, which depends on its feature
> configuration that is configured by KVM_ARM_VCPU_INIT (or other APIs).
>
> Of course there are other ways to achieve the same, and it's entirely
> possible to have a single function though. I just chose to use a
> separate function for each of those two different purposes.
OK fair enough. Was thinking that maybe it would simplify the code if we
had a single 'reset" cb but up to you.
Thanks
Eric
>
> Thanks,
> Reiji
>
