On Sun, Feb 13, 2022 at 10:57:22PM -0800, 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.
>
> kvm_set_id_reg_feature(), which is introduced in this patch,
> is going to be used by the following patch outsdie from sys_regs.c
typo: outside
> when an ID register field needs to be updated.
>
> Signed-off-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
> ---
> arch/arm64/include/asm/kvm_host.h | 1 +
> arch/arm64/include/asm/sysreg.h | 1 +
> arch/arm64/kvm/sys_regs.c | 280 ++++++++++++++++++++++++++++--
> 3 files changed, 268 insertions(+), 14 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index c041e5afe3d2..9ffe6604a58a 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -747,6 +747,7 @@ long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
> struct kvm_arm_copy_mte_tags *copy_tags);
>
> void set_default_id_regs(struct kvm *kvm);
> +int kvm_set_id_reg_feature(struct kvm *kvm, u32 id, u8 field_shift, u8 fval);
>
> /* Guest/host FPSIMD coordination helpers */
> int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu);
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 898bee0004ae..3f12e7036985 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -1214,6 +1214,7 @@
> #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)
nit: use GENMASK_ULL()
> /* 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))
nit: make use of the newly-minted ARM64_FEATURE_FIELD_MASK in this
macro.
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 080908c60fa6..da76516f2aad 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -265,6 +265,113 @@ static bool trap_raz_wi(struct kvm_vcpu *vcpu,
> return read_zero(vcpu, p);
> }
>
> +struct id_reg_info {
> + /* Register ID */
> + u32 sys_reg;
> +
> + /*
> + * Limit value of the register for a vcpu. The value is the sanitized
> + * system value with bits set/cleared for unsupported features for the
> + * guest.
> + */
> + u64 vcpu_limit_val;
> +
> + /* Fields that are not validated by arm64_check_features_kvm. */
> + u64 ignore_mask;
> +
> + /* An optional initialization function of the id_reg_info */
> + void (*init)(struct id_reg_info *id_reg);
> +
> + /*
> + * This is an optional ID register specific validation function. When
> + * userspace tries to set the ID register, arm64_check_features_kvm()
> + * will check if the requested value indicates any features that cannot
> + * be supported by KVM on the host. But, some ID register fields need
> + * a special checking, and this function can be used for such fields.
> + * e.g. When SVE is configured for a vCPU by KVM_ARM_VCPU_INIT,
> + * ID_AA64PFR0_EL1.SVE shouldn't be set to 0 for the vCPU.
> + * The validation function for ID_AA64PFR0_EL1 could be used to check
> + * the field is consistent with SVE configuration.
> + */
> + int (*validate)(struct kvm_vcpu *vcpu, const struct id_reg_info *id_reg,
> + u64 val);
> +
> + /*
> + * Return a bitmask of the vCPU's ID register fields that are not
> + * synced with saved (per VM) ID register value, which usually
> + * indicates opt-in CPU features that are not configured for the vCPU.
> + * ID registers are saved per VM, but some opt-in CPU features can
> + * be configured per vCPU. The saved (per VM) values for such
> + * features are for vCPUs with the features (and zero for
> + * vCPUs without the features).
> + * Return value of this function is used to handle such fields
> + * for per vCPU ID register read/write request with saved per VM
> + * ID register. See the __write_id_reg's comment for more detail.
> + */
> + u64 (*vcpu_mask)(const struct kvm_vcpu *vcpu,
> + const struct id_reg_info *id_reg);
> +};
> +
> +static void id_reg_info_init(struct id_reg_info *id_reg)
> +{
> + u64 val = read_sanitised_ftr_reg(id_reg->sys_reg);
> +
> + id_reg->vcpu_limit_val = val;
> + if (id_reg->init)
> + id_reg->init(id_reg);
> +
> + /*
> + * id_reg->init() might update id_reg->vcpu_limit_val.
> + * Make sure that id_reg->vcpu_limit_val, which will be the default
> + * register value for guests, is a safe value to use for guests
> + * on the host.
> + */
> + WARN_ON_ONCE(arm64_check_features_kvm(id_reg->sys_reg,
> + id_reg->vcpu_limit_val, val));
> +}
> +
> +/*
> + * An ID register that needs special handling to control the value for the
> + * guest must have its own id_reg_info in id_reg_info_table.
> + * (i.e. the reset value is different from the host's sanitized value,
> + * the value is affected by opt-in features, some fields need specific
> + * validation, etc.)
> + */
> +#define GET_ID_REG_INFO(id) (id_reg_info_table[IDREG_IDX(id)])
> +static struct id_reg_info *id_reg_info_table[KVM_ARM_ID_REG_MAX_NUM] = {};
It seems a bit peculiar that we effectively have two arrays that
describe feature ID registers now. IMO, it might be a bit cleaner to
sweep all relevant data into this array and just remove them from the
general system register array altogether.
We are already adding a lot of special-case handling for feature ID
registers, and that is only bound to increase as the architecture is
extended upon further.
> +static int validate_id_reg(struct kvm_vcpu *vcpu, u32 id, u64 val)
> +{
> + const struct id_reg_info *id_reg = GET_ID_REG_INFO(id);
> + u64 limit, tmp_val;
> + int err;
> +
> + if (id_reg) {
> + limit = id_reg->vcpu_limit_val;
> + /*
> + * Replace the fields that are indicated in ignore_mask with
> + * the value in the limit to not have arm64_check_features_kvm()
> + * check the field in @val.
> + */
> + tmp_val = val & ~id_reg->ignore_mask;
> + tmp_val |= (limit & id_reg->ignore_mask);
> + } else {
> + limit = read_sanitised_ftr_reg(id);
> + tmp_val = val;
> + }
> +
> + /* Check if the value indicates any feature that is not in the limit. */
> + err = arm64_check_features_kvm(id, tmp_val, limit);
> + if (err)
> + return err;
> +
> + if (id_reg && id_reg->validate)
> + /* Run the ID register specific validity check. */
> + err = id_reg->validate(vcpu, id_reg, val);
> +
> + return err;
> +}
> +
> /*
> * ARMv8.1 mandates at least a trivial LORegion implementation, where all the
> * RW registers are RES0 (which we can implement as RAZ/WI). On an ARMv8.0
> @@ -1068,9 +1175,91 @@ static bool is_id_reg(u32 id)
> sys_reg_CRm(id) < 8);
> }
>
> +static u64 read_kvm_id_reg(struct kvm *kvm, u32 id)
> +{
> + return kvm->arch.id_regs[IDREG_IDX(id)];
> +}
> +
> +static int __modify_kvm_id_reg(struct kvm *kvm, u32 id, u64 val,
> + u64 preserve_mask)
> +{
> + u64 old, new;
> +
> + lockdep_assert_held(&kvm->lock);
> +
> + old = kvm->arch.id_regs[IDREG_IDX(id)];
> +
> + /* Preserve the value at the bit position set in preserve_mask */
> + new = old & preserve_mask;
> + new |= (val & ~preserve_mask);
> +
> + /* Don't allow to modify ID register value after KVM_RUN on any vCPUs */
> + if (kvm->arch.ran_once && new != old)
> + return -EBUSY;
> +
> + WRITE_ONCE(kvm->arch.id_regs[IDREG_IDX(id)], new);
> +
> + return 0;
> +}
> +
> +static int modify_kvm_id_reg(struct kvm *kvm, u32 id, u64 val,
> + u64 preserve_mask)
> +{
> + int ret;
> +
> + mutex_lock(&kvm->lock);
> + ret = __modify_kvm_id_reg(kvm, id, val, preserve_mask);
> + mutex_unlock(&kvm->lock);
> +
> + return ret;
> +}
> +
> +static int write_kvm_id_reg(struct kvm *kvm, u32 id, u64 val)
> +{
> + return modify_kvm_id_reg(kvm, id, val, 0);
> +}
> +
> +/*
> + * KVM basically forces all vCPUs of the guest to have a uniform value for
> + * each ID register (it means KVM_SET_ONE_REG for a vCPU affects all
> + * the vCPUs of the guest), and the id_regs[] of kvm_arch holds values
> + * of ID registers for the guest. However, there is an exception for
> + * ID register fields corresponding to CPU features that can be
> + * configured per vCPU by KVM_ARM_VCPU_INIT, or etc (e.g. PMUv3, SVE, etc).
> + * For such fields, all vCPUs that have the feature will have a non-zero
> + * uniform value, which can be updated by userspace, but the vCPUs that
> + * don't have the feature will have zero for the fields.
> + * Values that @id_regs holds are for vCPUs that have such features. So,
> + * to get the ID register value for a vCPU that doesn't have those features,
> + * the corresponding fields in id_regs[] needs to be cleared.
> + * A bitmask of the fields are provided by id_reg_info's vcpu_mask(), and
> + * __write_id_reg() and __read_id_reg() take care of those fields using
> + * the bitmask.
> + */
> +static int __write_id_reg(struct kvm_vcpu *vcpu, u32 id, u64 val)
> +{
> + const struct id_reg_info *id_reg = GET_ID_REG_INFO(id);
> + u64 mask = 0;
> +
> + if (id_reg && id_reg->vcpu_mask)
> + mask = id_reg->vcpu_mask(vcpu, id_reg);
> +
> + /*
> + * Update the ID register for the guest with @val, except for fields
> + * that are set in the mask, which indicates fields for opt-in
> + * features that are not configured for the vCPU.
> + */
> + return modify_kvm_id_reg(vcpu->kvm, id, val, mask);
> +}
> +
> static u64 __read_id_reg(const struct kvm_vcpu *vcpu, u32 id)
> {
> - u64 val = vcpu->kvm->arch.id_regs[IDREG_IDX(id)];
> + const struct id_reg_info *id_reg = GET_ID_REG_INFO(id);
> + u64 val = read_kvm_id_reg(vcpu->kvm, id);
> +
> + if (id_reg && id_reg->vcpu_mask)
> + /* Clear fields for opt-in features that are not configured. */
> + val &= ~(id_reg->vcpu_mask(vcpu, id_reg));
>
> switch (id) {
> case SYS_ID_AA64PFR0_EL1:
> @@ -1229,12 +1418,7 @@ static int set_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
> return 0;
> }
>
> -/*
> - * cpufeature ID register user accessors
> - *
> - * For now, these registers are immutable for userspace, so for set_id_reg()
> - * we don't allow the effective value to be changed.
> - */
> +/* cpufeature ID register user accessors */
> static int __get_id_reg(const struct kvm_vcpu *vcpu,
> const struct sys_reg_desc *rd, void __user *uaddr,
> bool raz)
> @@ -1245,11 +1429,31 @@ static int __get_id_reg(const struct kvm_vcpu *vcpu,
> return reg_to_user(uaddr, &val, id);
> }
>
> -static int __set_id_reg(const struct kvm_vcpu *vcpu,
> +/*
> + * Check if the given id indicates AArch32 ID register encoding.
> + */
> +static bool is_aarch32_id_reg(u32 id)
> +{
> + u32 crm, op2;
> +
> + if (!is_id_reg(id))
> + return false;
> +
> + crm = sys_reg_CRm(id);
> + op2 = sys_reg_Op2(id);
> + if (crm == 1 || crm == 2 || (crm == 3 && (op2 != 3 && op2 != 7)))
> + /* AArch32 ID register */
> + return true;
> +
> + return false;
> +}
> +
> +static int __set_id_reg(struct kvm_vcpu *vcpu,
> const struct sys_reg_desc *rd, void __user *uaddr,
> bool raz)
> {
> const u64 id = sys_reg_to_index(rd);
> + u32 encoding = reg_to_encoding(rd);
> int err;
> u64 val;
>
> @@ -1257,11 +1461,28 @@ static int __set_id_reg(const struct kvm_vcpu *vcpu,
> if (err)
> return err;
>
> - /* This is what we mean by invariant: you can't change it. */
> - if (val != read_id_reg(vcpu, rd, raz))
> + if (val == read_id_reg(vcpu, rd, raz))
> + /* The value is same as the current value. Nothing to do. */
> + return 0;
> +
> + /*
> + * Don't allow to modify the register's value if the register is raz,
> + * or the reg doesn't have the id_reg_info.
> + */
> + if (raz || !GET_ID_REG_INFO(encoding))
> return -EINVAL;
>
> - return 0;
> + /*
> + * Skip the validation of AArch32 ID registers if the system doesn't
> + * 32bit EL0 (their value are UNKNOWN).
> + */
> + if (system_supports_32bit_el0() || !is_aarch32_id_reg(encoding)) {
> + err = validate_id_reg(vcpu, encoding, val);
> + if (err)
> + return err;
> + }
> +
> + return __write_id_reg(vcpu, encoding, val);
> }
>
> static int get_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
> @@ -2823,6 +3044,20 @@ int kvm_arm_copy_sys_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
> return write_demux_regids(uindices);
> }
>
> +static void id_reg_info_init_all(void)
> +{
> + int i;
> + struct id_reg_info *id_reg;
> +
> + for (i = 0; i < ARRAY_SIZE(id_reg_info_table); i++) {
> + id_reg = (struct id_reg_info *)id_reg_info_table[i];
> + if (!id_reg)
> + continue;
> +
> + id_reg_info_init(id_reg);
> + }
> +}
> +
> void kvm_sys_reg_table_init(void)
> {
> unsigned int i;
> @@ -2857,6 +3092,8 @@ void kvm_sys_reg_table_init(void)
> break;
> /* Clear all higher bits. */
> cache_levels &= (1 << (i*3))-1;
> +
> + id_reg_info_init_all();
> }
>
> /*
> @@ -2869,11 +3106,12 @@ void set_default_id_regs(struct kvm *kvm)
> u32 id;
> const struct sys_reg_desc *rd;
> u64 val;
> + struct id_reg_info *idr;
>
> for (i = 0; i < ARRAY_SIZE(sys_reg_descs); i++) {
> rd = &sys_reg_descs[i];
> if (rd->access != access_id_reg)
> - /* Not ID register, or hidden/reserved ID register */
> + /* Not ID register or hidden/reserved ID register */
> continue;
>
> id = reg_to_encoding(rd);
> @@ -2881,7 +3119,21 @@ void set_default_id_regs(struct kvm *kvm)
> /* Shouldn't happen */
> continue;
>
> - val = read_sanitised_ftr_reg(id);
> - kvm->arch.id_regs[IDREG_IDX(id)] = val;
> + idr = GET_ID_REG_INFO(id);
> + val = idr ? idr->vcpu_limit_val : read_sanitised_ftr_reg(id);
> + WARN_ON_ONCE(write_kvm_id_reg(kvm, id, val));
> }
> }
> +
> +/*
> + * Update the ID register's field with @fval for the guest.
> + * The caller is expected to hold the kvm->lock.
> + * This will not fail unless any vCPUs in the guest have started.
> + */
> +int kvm_set_id_reg_feature(struct kvm *kvm, u32 id, u8 field_shift, u8 fval)
> +{
> + u64 val = ((u64)fval & ARM64_FEATURE_FIELD_MASK) << field_shift;
> + u64 preserve_mask = ~(ARM64_FEATURE_FIELD_MASK << field_shift);
> +
> + return __modify_kvm_id_reg(kvm, id, val, preserve_mask);
> +}
> --
> 2.35.1.265.g69c8d7142f-goog
>
--
Thanks,
Oliver
