[PATCH v4 2/6] KVM: arm64: Save ID registers' sanitized value per guest
Jing Zhang
jingzhangos at google.com
Tue Mar 28 10:36:58 PDT 2023
Hi Marc,
On Mon, Mar 27, 2023 at 3:15 AM Marc Zyngier <maz at kernel.org> wrote:
>
> On Fri, 17 Mar 2023 05:06:33 +0000,
> Jing Zhang <jingzhangos at google.com> wrote:
> >
> > From: Reiji Watanabe <reijiw at google.com>
> >
> > 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).
> >
> > No functional change intended.
> >
> > Signed-off-by: Reiji Watanabe <reijiw at google.com>
> > Co-developed-by: Jing Zhang <jingzhangos at google.com>
> > Signed-off-by: Jing Zhang <jingzhangos at google.com>
> > ---
> > arch/arm64/include/asm/kvm_host.h | 11 ++++++++
> > arch/arm64/kvm/arm.c | 1 +
> > arch/arm64/kvm/id_regs.c | 44 ++++++++++++++++++++++++-------
> > arch/arm64/kvm/sys_regs.c | 2 +-
> > arch/arm64/kvm/sys_regs.h | 1 +
> > 5 files changed, 49 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index a1892a8f6032..fb6b50b1f111 100644
> > --- a/arch/arm64/include/asm/kvm_host.h
> > +++ b/arch/arm64/include/asm/kvm_host.h
> > @@ -245,6 +245,15 @@ struct kvm_arch {
> > * the associated pKVM instance in the hypervisor.
> > */
> > struct kvm_protected_vm pkvm;
> > +
> > + /*
> > + * Save ID registers for the guest in id_regs[].
> > + * (Op0, Op1, CRn, CRm, Op2) of the ID registers to be saved in it
> > + * is (3, 0, 0, crm, op2), where 1<=crm<8, 0<=op2<8.
> > + */
> > +#define KVM_ARM_ID_REG_NUM 56
> > +#define IDREG_IDX(id) (((sys_reg_CRm(id) - 1) << 3) | sys_reg_Op2(id))
> > + u64 id_regs[KVM_ARM_ID_REG_NUM];
>
> Place these registers in their own structure, and place this structure
> *before* the pvm structure. Document what guards these registers when
> updated (my hunch is that this should rely on Oliver's locking fixes
> if the update comes from a vcpu).
Sure, I will put them in their own structure and place it before the
pkvm structure.
IIUC, usually we don't need a specific locking to update idregs here.
All idregs are 64 bit and can be read/written atomically. The only
case that may need a locking is to keep the consistency for PMUVer in
AA64DFR0_EL1 and PerfMon in DFR0_EL1. If there is no use case for two
VCPU threads in a VM to update PMUVer and PerfMon concurrently, then
we don't need the locking as in later patch by using the kvm lock.
WDTY?
>
> > };
> >
> > struct kvm_vcpu_fault_info {
> > @@ -1005,6 +1014,8 @@ 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 kvm_arm_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 3bd732eaf087..4579c878ab30 100644
> > --- a/arch/arm64/kvm/arm.c
> > +++ b/arch/arm64/kvm/arm.c
> > @@ -153,6 +153,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
> >
> > set_default_spectre(kvm);
> > kvm_arm_init_hypercalls(kvm);
> > + kvm_arm_set_default_id_regs(kvm);
> >
> > /*
> > * Initialise the default PMUver before there is a chance to
> > diff --git a/arch/arm64/kvm/id_regs.c b/arch/arm64/kvm/id_regs.c
> > index 08b738852955..e393b5730557 100644
> > --- a/arch/arm64/kvm/id_regs.c
> > +++ b/arch/arm64/kvm/id_regs.c
> > @@ -52,16 +52,9 @@ static u8 pmuver_to_perfmon(u8 pmuver)
> > }
> > }
> >
> > -/* 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)
> > +u64 kvm_arm_read_id_reg(const struct kvm_vcpu *vcpu, u32 id)
> > {
> > - u32 id = reg_to_encoding(r);
> > - u64 val;
> > -
> > - if (sysreg_visible_as_raz(vcpu, r))
> > - 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:
> > @@ -126,6 +119,14 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu, struct sys_reg_desc const *r
> > return val;
> > }
> >
> > +static u64 read_id_reg(const struct kvm_vcpu *vcpu, struct sys_reg_desc const *r)
> > +{
> > + if (sysreg_visible_as_raz(vcpu, r))
> > + return 0;
> > +
> > + return kvm_arm_read_id_reg(vcpu, reg_to_encoding(r));
> > +}
> > +
> > /* cpufeature ID register access trap handlers */
> >
> > static bool access_id_reg(struct kvm_vcpu *vcpu,
> > @@ -504,3 +505,28 @@ int kvm_arm_walk_id_regs(struct kvm_vcpu *vcpu, u64 __user *uind)
> > }
> > return total;
> > }
> > +
> > +/*
> > + * Set the guest's ID registers that are defined in id_reg_descs[]
> > + * with ID_SANITISED() to the host's sanitized value.
> > + */
> > +void kvm_arm_set_default_id_regs(struct kvm *kvm)
> > +{
> > + int i;
> > + u32 id;
> > + u64 val;
> > +
> > + for (i = 0; i < ARRAY_SIZE(id_reg_descs); i++) {
> > + id = reg_to_encoding(&id_reg_descs[i]);
> > + if (WARN_ON_ONCE(!is_id_reg(id)))
> > + /* Shouldn't happen */
> > + continue;
> > +
> > + if (id_reg_descs[i].visibility == raz_visibility)
> > + /* Hidden or reserved ID register */
> > + continue;
>
> Relying on function pointer comparison is really fragile. If I wrap
> raz_visibility() in another function, this won't catch it. It also
> doesn't bode well with your 'inline' definition of this function.
>
> More importantly, why do we care about checking for visibility at all?
> We can happily populate the array and rely on the runtime visibility.
Right. I'll remove this checking.
>
> > +
> > + val = read_sanitised_ftr_reg(id);
> > + kvm->arch.id_regs[IDREG_IDX(id)] = val;
> > + }
> > +}
>
> Thanks,
>
> M.
>
> --
> Without deviation from the norm, progress is not possible.
Thanks,
Jing
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