Re: [PATCH v5 08/20] RISC-V: KVM: Implement KVM_GET_ONE_REG/KVM_SET_ONE_REG ioctls

Anup Patel
2019-08-22T14:06:19Z

On Thu, Aug 22, 2019 at 5:31 PM Alexander Graf <graf@amazon.com> wrote:
>
> On 22.08.19 10:44, Anup Patel wrote:
> > For KVM RISC-V, we use KVM_GET_ONE_REG/KVM_SET_ONE_REG ioctls to access
> > VCPU config and registers from user-space.
> >
> > We have three types of VCPU registers:
> > 1. CONFIG - these are VCPU config and capabilities
> > 2. CORE - these are VCPU general purpose registers
> > 3. CSR - these are VCPU control and status registers
> >
> > The CONFIG registers available to user-space are ISA and TIMEBASE. Out
> > of these, TIMEBASE is a read-only register which inform user-space about
> > VCPU timer base frequency. The ISA register is a read and write register
> > where user-space can only write the desired VCPU ISA capabilities before
> > running the VCPU.
> >
> > The CORE registers available to user-space are PC, RA, SP, GP, TP, A0-A7,
> > T0-T6, S0-S11 and MODE. Most of these are RISC-V general registers except
> > PC and MODE. The PC register represents program counter whereas the MODE
> > register represent VCPU privilege mode (i.e. S/U-mode).
> >
> > The CSRs available to user-space are SSTATUS, SIE, STVEC, SSCRATCH, SEPC,
> > SCAUSE, STVAL, SIP, and SATP. All of these are read/write registers.
> >
> > In future, more VCPU register types will be added (such as FP) for the
> > KVM_GET_ONE_REG/KVM_SET_ONE_REG ioctls.
> >
> > Signed-off-by: Anup Patel <anup.patel@wdc.com>
> > Acked-by: Paolo Bonzini <pbonzini@redhat.com>
> > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> > ---
> > arch/riscv/include/uapi/asm/kvm.h | 40 ++++-
> > arch/riscv/kvm/vcpu.c | 235 +++++++++++++++++++++++++++++-
> > 2 files changed, 272 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> > index 6dbc056d58ba..024f220eb17e 100644
> > --- a/arch/riscv/include/uapi/asm/kvm.h
> > +++ b/arch/riscv/include/uapi/asm/kvm.h
> > @@ -23,8 +23,15 @@
> >
> > /* for KVM_GET_REGS and KVM_SET_REGS */
> > struct kvm_regs {
> > + /* out (KVM_GET_REGS) / in (KVM_SET_REGS) */
> > + struct user_regs_struct regs;
> > + unsigned long mode;
>
> Is there any particular reason you're reusing kvm_regs and don't invent
> your own struct? kvm_regs is explicitly meant for the get_regs and
> set_regs ioctls.
>
> > };
> >
> > +/* Possible privilege modes for kvm_regs */
> > +#define KVM_RISCV_MODE_S 1
> > +#define KVM_RISCV_MODE_U 0
> > +
> > /* for KVM_GET_FPU and KVM_SET_FPU */
> > struct kvm_fpu {
> > };
> > @@ -41,10 +48,41 @@ struct kvm_guest_debug_arch {
> > struct kvm_sync_regs {
> > };
> >
> > -/* dummy definition */
> > +/* for KVM_GET_SREGS and KVM_SET_SREGS */
> > struct kvm_sregs {
> > + unsigned long sstatus;
> > + unsigned long sie;
> > + unsigned long stvec;
> > + unsigned long sscratch;
> > + unsigned long sepc;
> > + unsigned long scause;
> > + unsigned long stval;
> > + unsigned long sip;
> > + unsigned long satp;
>
> Same comment here.
>
> > };
> >
> > +#define KVM_REG_SIZE(id) \
> > + (1U << (((id) & KVM_REG_SIZE_MASK) >> KVM_REG_SIZE_SHIFT))
> > +
> > +/* If you need to interpret the index values, here is the key: */
> > +#define KVM_REG_RISCV_TYPE_MASK 0x00000000FF000000
> > +#define KVM_REG_RISCV_TYPE_SHIFT 24
> > +
> > +/* Config registers are mapped as type 1 */
> > +#define KVM_REG_RISCV_CONFIG (0x01 << KVM_REG_RISCV_TYPE_SHIFT)
> > +#define KVM_REG_RISCV_CONFIG_ISA 0x0
> > +#define KVM_REG_RISCV_CONFIG_TIMEBASE 0x1
> > +
> > +/* Core registers are mapped as type 2 */
> > +#define KVM_REG_RISCV_CORE (0x02 << KVM_REG_RISCV_TYPE_SHIFT)
> > +#define KVM_REG_RISCV_CORE_REG(name) \
> > + (offsetof(struct kvm_regs, name) / sizeof(unsigned long))
>
> I see, you're trying to implicitly use the struct offsets as index.
>
> I'm not a really big fan of it, but I can't pinpoint exactly why just
> yet. It just seems too magical (read: potentially breaking down the
> road) for me.
>
> > +
> > +/* Control and status registers are mapped as type 3 */
> > +#define KVM_REG_RISCV_CSR (0x03 << KVM_REG_RISCV_TYPE_SHIFT)
> > +#define KVM_REG_RISCV_CSR_REG(name) \
> > + (offsetof(struct kvm_sregs, name) / sizeof(unsigned long))
> > +
> > #endif
> >
> > #endif /* __LINUX_KVM_RISCV_H */
> > diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> > index 7f59e85c6af8..9396a83c0611 100644
> > --- a/arch/riscv/kvm/vcpu.c
> > +++ b/arch/riscv/kvm/vcpu.c
> > @@ -164,6 +164,215 @@ vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
> > return VM_FAULT_SIGBUS;
> > }
> >
> > +static int kvm_riscv_vcpu_get_reg_config(struct kvm_vcpu *vcpu,
> > + const struct kvm_one_reg *reg)
> > +{
> > + unsigned long __user *uaddr =
> > + (unsigned long __user *)(unsigned long)reg->addr;
> > + unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
> > + KVM_REG_SIZE_MASK |
> > + KVM_REG_RISCV_CONFIG);
> > + unsigned long reg_val;
> > +
> > + if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
> > + return -EINVAL;
> > +
> > + switch (reg_num) {
> > + case KVM_REG_RISCV_CONFIG_ISA:
> > + reg_val = vcpu->arch.isa;
> > + break;
> > + case KVM_REG_RISCV_CONFIG_TIMEBASE:
> > + reg_val = riscv_timebase;
>
> What does this reflect? The current guest time hopefully not? An offset?
> Related to what?
>
> All ONE_REG registers should be documented in
> Documentation/virtual/kvm/api.txt. Please add them there.
>
> > + break;
> > + default:
> > + return -EINVAL;
> > + };
> > +
> > + if (copy_to_user(uaddr, &reg_val, KVM_REG_SIZE(reg->id)))
> > + return -EFAULT;
> > +
> > + return 0;
> > +}
> > +
> > +static int kvm_riscv_vcpu_set_reg_config(struct kvm_vcpu *vcpu,
> > + const struct kvm_one_reg *reg)
> > +{
> > + unsigned long __user *uaddr =
> > + (unsigned long __user *)(unsigned long)reg->addr;
> > + unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
> > + KVM_REG_SIZE_MASK |
> > + KVM_REG_RISCV_CONFIG);
> > + unsigned long reg_val;
> > +
> > + if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
> > + return -EINVAL;
> > +
> > + if (copy_from_user(&reg_val, uaddr, KVM_REG_SIZE(reg->id)))
> > + return -EFAULT;
> > +
> > + switch (reg_num) {
> > + case KVM_REG_RISCV_CONFIG_ISA:
> > + if (!vcpu->arch.ran_atleast_once) {
> > + vcpu->arch.isa = reg_val;
> > + vcpu->arch.isa &= riscv_isa_extension_base(NULL);
> > + vcpu->arch.isa &= KVM_RISCV_ISA_ALLOWED;
>
> This register definitely needs proper documentation too ;). You may want
> to reconsider to put a few of the helper bits from patch 02/20 into
> uapi, so that user space can directly use them.
>
> > + } else {
> > + return -ENOTSUPP;
> > + }
> > + break;
> > + case KVM_REG_RISCV_CONFIG_TIMEBASE:
> > + return -ENOTSUPP;
> > + default:
> > + return -EINVAL;
> > + };
> > +
> > + return 0;
> > +}
> > +
> > +static int kvm_riscv_vcpu_get_reg_core(struct kvm_vcpu *vcpu,
> > + const struct kvm_one_reg *reg)
> > +{
> > + struct kvm_cpu_context *cntx = &vcpu->arch.guest_context;
> > + unsigned long __user *uaddr =
> > + (unsigned long __user *)(unsigned long)reg->addr;
> > + unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
> > + KVM_REG_SIZE_MASK |
> > + KVM_REG_RISCV_CORE);
> > + unsigned long reg_val;
> > +
> > + if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
> > + return -EINVAL;
> > +
> > + if (reg_num == KVM_REG_RISCV_CORE_REG(regs.pc))
> > + reg_val = cntx->sepc;
> > + else if (KVM_REG_RISCV_CORE_REG(regs.pc) < reg_num &&
> > + reg_num <= KVM_REG_RISCV_CORE_REG(regs.t6))
> > + reg_val = ((unsigned long *)cntx)[reg_num];
> > + else if (reg_num == KVM_REG_RISCV_CORE_REG(mode))
> > + reg_val = (cntx->sstatus & SR_SPP) ?
> > + KVM_RISCV_MODE_S : KVM_RISCV_MODE_U;
> > + else
> > + return -EINVAL;
> > +
> > + if (copy_to_user(uaddr, &reg_val, KVM_REG_SIZE(reg->id)))
> > + return -EFAULT;
> > +
> > + return 0;
> > +}
> > +
> > +static int kvm_riscv_vcpu_set_reg_core(struct kvm_vcpu *vcpu,
> > + const struct kvm_one_reg *reg)
> > +{
> > + struct kvm_cpu_context *cntx = &vcpu->arch.guest_context;
> > + unsigned long __user *uaddr =
> > + (unsigned long __user *)(unsigned long)reg->addr;
> > + unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
> > + KVM_REG_SIZE_MASK |
> > + KVM_REG_RISCV_CORE);
> > + unsigned long reg_val;
> > +
> > + if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
> > + return -EINVAL;
> > +
> > + if (copy_from_user(&reg_val, uaddr, KVM_REG_SIZE(reg->id)))
> > + return -EFAULT;
> > +
> > + if (reg_num == KVM_REG_RISCV_CORE_REG(regs.pc))
> > + cntx->sepc = reg_val;
> > + else if (KVM_REG_RISCV_CORE_REG(regs.pc) < reg_num &&
> > + reg_num <= KVM_REG_RISCV_CORE_REG(regs.t6))
> > + ((unsigned long *)cntx)[reg_num] = reg_val;
> > + else if (reg_num == KVM_REG_RISCV_CORE_REG(mode)) {
> > + if (reg_val == KVM_RISCV_MODE_S)
> > + cntx->sstatus |= SR_SPP;
> > + else
> > + cntx->sstatus &= ~SR_SPP;
> > + } else
> > + return -EINVAL;
> > +
> > + return 0;
> > +}
> > +
> > +static int kvm_riscv_vcpu_get_reg_csr(struct kvm_vcpu *vcpu,
> > + const struct kvm_one_reg *reg)
> > +{
> > + struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
> > + unsigned long __user *uaddr =
> > + (unsigned long __user *)(unsigned long)reg->addr;
> > + unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
> > + KVM_REG_SIZE_MASK |
> > + KVM_REG_RISCV_CSR);
> > + unsigned long reg_val;
> > +
> > + if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
> > + return -EINVAL;
> > + if (reg_num >= sizeof(struct kvm_sregs) / sizeof(unsigned long))
> > + return -EINVAL;
> > +
> > + if (reg_num == KVM_REG_RISCV_CSR_REG(sip))
> > + kvm_riscv_vcpu_flush_interrupts(vcpu);
> > +
> > + reg_val = ((unsigned long *)csr)[reg_num];
> > +
> > + if (copy_to_user(uaddr, &reg_val, KVM_REG_SIZE(reg->id)))
> > + return -EFAULT;
> > +
> > + return 0;
> > +}
> > +
> > +static int kvm_riscv_vcpu_set_reg_csr(struct kvm_vcpu *vcpu,
> > + const struct kvm_one_reg *reg)
> > +{
> > + struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;
> > + unsigned long __user *uaddr =
> > + (unsigned long __user *)(unsigned long)reg->addr;
> > + unsigned long reg_num = reg->id & ~(KVM_REG_ARCH_MASK |
> > + KVM_REG_SIZE_MASK |
> > + KVM_REG_RISCV_CSR);
> > + unsigned long reg_val;
> > +
> > + if (KVM_REG_SIZE(reg->id) != sizeof(unsigned long))
> > + return -EINVAL;
> > + if (reg_num >= sizeof(struct kvm_sregs) / sizeof(unsigned long))
> > + return -EINVAL;
> > +
> > + if (copy_from_user(&reg_val, uaddr, KVM_REG_SIZE(reg->id)))
> > + return -EFAULT;
> > +
> > + ((unsigned long *)csr)[reg_num] = reg_val;
> > +
> > + if (reg_num == KVM_REG_RISCV_CSR_REG(sip))
> > + WRITE_ONCE(vcpu->arch.irqs_pending_mask, 0);
>
> Why does writing SIP clear all pending interrupts?

irqs_pending_mask represents bits changes in irqs_pending.

Once the SIP CSR is updated by user-space, the changes to
irqs_pending are no longer valid so we clear irqs_pending_mask.

If we don't clear irqs_pending_mask then value programmed by
user-space can get overwritten if there were interrupts after
we saved SIP CSR and before we restored it.

Regards,
Anup

>
>
> Alex