[RFC PATCH v4 02/26] KVM: arm64: Save ID registers' sanitized value per guest
Fuad Tabba
tabba at google.com
Mon Jan 24 08:21:32 PST 2022
Hi Reiji,
On Thu, Jan 6, 2022 at 4:28 AM Reiji Watanabe <reijiw at google.com> wrote:
>
> Introduce id_regs[] in kvm_arch as a storage of guest's ID registers,
> and save ID registers' sanitized value in the array at KVM_CREATE_VM.
> Use the saved ones when ID registers are read by the guest or
> userspace (via KVM_GET_ONE_REG).
>
> Signed-off-by: Reiji Watanabe <reijiw at google.com>
> ---
> arch/arm64/include/asm/kvm_host.h | 16 ++++++++
> arch/arm64/kvm/arm.c | 1 +
> arch/arm64/kvm/sys_regs.c | 62 ++++++++++++++++++++++---------
> 3 files changed, 62 insertions(+), 17 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 2a5f7f38006f..c789a0137f58 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -102,6 +102,17 @@ struct kvm_s2_mmu {
> struct kvm_arch_memory_slot {
> };
>
> +/*
> + * (Op0, Op1, CRn, CRm, Op2) of ID registers is (3, 0, 0, crm, op2),
> + * where 0<=crm<8, 0<=op2<8.
> + */
> +#define KVM_ARM_ID_REG_MAX_NUM 64
> +#define IDREG_IDX(id) ((sys_reg_CRm(id) << 3) | sys_reg_Op2(id))
> +#define is_id_reg(id) \
> + (sys_reg_Op0(id) == 3 && sys_reg_Op1(id) == 0 && \
> + sys_reg_CRn(id) == 0 && sys_reg_CRm(id) >= 0 && \
> + sys_reg_CRm(id) < 8)
> +
This is consistent with the Arm ARM "Table D12-2 System instruction
encodings for non-Debug System register accesses".
Minor nit, would it be better to have IDREG_IDX and is_id_reg in
arch/arm64/kvm/sys_regs.h, since other similar and related ones are
there?
> struct kvm_arch {
> struct kvm_s2_mmu mmu;
>
> @@ -137,6 +148,9 @@ struct kvm_arch {
>
> /* Memory Tagging Extension enabled for the guest */
> bool mte_enabled;
> +
> + /* ID registers for the guest. */
> + u64 id_regs[KVM_ARM_ID_REG_MAX_NUM];
> };
>
> struct kvm_vcpu_fault_info {
> @@ -734,6 +748,8 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
> 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);
> +
> /* Guest/host FPSIMD coordination helpers */
> int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu);
> void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu);
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index e4727dc771bf..5f497a0af254 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -156,6 +156,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> kvm->arch.max_vcpus = kvm_arm_default_max_vcpus();
>
> set_default_spectre(kvm);
> + set_default_id_regs(kvm);
>
> return ret;
> out_free_stage2_pgd:
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index e3ec1a44f94d..80dc62f98ef0 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -33,6 +33,8 @@
>
> #include "trace.h"
>
> +static u64 __read_id_reg(const struct kvm_vcpu *vcpu, u32 id);
> +
> /*
> * All of this file is extremely similar to the ARM coproc.c, but the
> * types are different. My gut feeling is that it should be pretty
> @@ -273,7 +275,7 @@ static bool trap_loregion(struct kvm_vcpu *vcpu,
> struct sys_reg_params *p,
> const struct sys_reg_desc *r)
> {
> - u64 val = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1);
> + u64 val = __read_id_reg(vcpu, SYS_ID_AA64MMFR1_EL1);
> u32 sr = reg_to_encoding(r);
>
> if (!(val & (0xfUL << ID_AA64MMFR1_LOR_SHIFT))) {
> @@ -1059,17 +1061,9 @@ static bool access_arch_timer(struct kvm_vcpu *vcpu,
> return true;
> }
>
> -/* Read a sanitised cpufeature ID register by sys_reg_desc */
> -static u64 read_id_reg(const struct kvm_vcpu *vcpu,
> - struct sys_reg_desc const *r, bool raz)
> +static u64 __read_id_reg(const struct kvm_vcpu *vcpu, u32 id)
> {
> - u32 id = reg_to_encoding(r);
> - u64 val;
> -
> - if (raz)
> - return 0;
> -
> - val = read_sanitised_ftr_reg(id);
> + u64 val = vcpu->kvm->arch.id_regs[IDREG_IDX(id)];
>
> switch (id) {
> case SYS_ID_AA64PFR0_EL1:
> @@ -1119,6 +1113,14 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
> return val;
> }
>
> +static u64 read_id_reg(const struct kvm_vcpu *vcpu,
> + struct sys_reg_desc const *r, bool raz)
> +{
> + u32 id = reg_to_encoding(r);
> +
> + return raz ? 0 : __read_id_reg(vcpu, id);
> +}
> +
> static unsigned int id_visibility(const struct kvm_vcpu *vcpu,
> const struct sys_reg_desc *r)
> {
> @@ -1223,9 +1225,8 @@ static int set_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
> /*
> * cpufeature ID register user accessors
> *
> - * For now, these registers are immutable for userspace, so no values
> - * are stored, and for set_id_reg() we don't allow the effective value
> - * to be changed.
> + * For now, these registers are immutable for userspace, so for set_id_reg()
> + * we don't allow the effective value to be changed.
> */
> static int __get_id_reg(const struct kvm_vcpu *vcpu,
> const struct sys_reg_desc *rd, void __user *uaddr,
> @@ -1237,7 +1238,7 @@ 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,
> +static int __set_id_reg(struct kvm_vcpu *vcpu,
> const struct sys_reg_desc *rd, void __user *uaddr,
> bool raz)
Minor nit: why remove the const in this patch? This is required for a
future patch but not for this one.
Thanks,
/fuad
> {
> @@ -1837,8 +1838,8 @@ static bool trap_dbgdidr(struct kvm_vcpu *vcpu,
> if (p->is_write) {
> return ignore_write(vcpu, p);
> } else {
> - u64 dfr = read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1);
> - u64 pfr = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1);
> + u64 dfr = __read_id_reg(vcpu, SYS_ID_AA64DFR0_EL1);
> + u64 pfr = __read_id_reg(vcpu, SYS_ID_AA64PFR0_EL1);
> u32 el3 = !!cpuid_feature_extract_unsigned_field(pfr, ID_AA64PFR0_EL3_SHIFT);
>
> p->regval = ((((dfr >> ID_AA64DFR0_WRPS_SHIFT) & 0xf) << 28) |
> @@ -2850,3 +2851,30 @@ void kvm_sys_reg_table_init(void)
> /* Clear all higher bits. */
> cache_levels &= (1 << (i*3))-1;
> }
> +
> +/*
> + * Set the guest's ID registers that are defined in sys_reg_descs[]
> + * with ID_SANITISED() to the host's sanitized value.
> + */
> +void set_default_id_regs(struct kvm *kvm)
> +{
> + int i;
> + u32 id;
> + const struct sys_reg_desc *rd;
> + u64 val;
> +
> + 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 */
> + continue;
> +
> + id = reg_to_encoding(rd);
> + if (WARN_ON_ONCE(!is_id_reg(id)))
> + /* Shouldn't happen */
> + continue;
> +
> + val = read_sanitised_ftr_reg(id);
> + kvm->arch.id_regs[IDREG_IDX(id)] = val;
> + }
> +}
> --
> 2.34.1.448.ga2b2bfdf31-goog
>
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