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Subject: Re: [PATCH v5 08/20] RISC-V: KVM: Implement
 KVM_GET_ONE_REG/KVM_SET_ONE_REG ioctls
To:     Anup Patel <Anup.Patel@wdc.com>,
        Palmer Dabbelt <palmer@sifive.com>,
        "Paul Walmsley" <paul.walmsley@sifive.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim K <rkrcmar@redhat.com>
CC:     Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Atish Patra <Atish.Patra@wdc.com>,
        Alistair Francis <Alistair.Francis@wdc.com>,
        Damien Le Moal <Damien.LeMoal@wdc.com>,
        "Christoph Hellwig" <hch@infradead.org>,
        Anup Patel <anup@brainfault.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20190822084131.114764-1-anup.patel@wdc.com>
 <20190822084131.114764-9-anup.patel@wdc.com>
From:   Alexander Graf <graf@amazon.com>
Message-ID: <d306ffaf-c9ac-4a9f-4382-95001487364d@amazon.com>
Date:   Thu, 22 Aug 2019 14:01:03 +0200
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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?


Alex