Re: [PATCH v4 3/3] arm64: kvm: inject SError with user space specified syndrome

Christoffer Dall
2017-07-03T08:38:50Z

Hi Dongjiu,

On Mon, Jun 26, 2017 at 08:46:39PM +0800, Dongjiu Geng wrote:
> when SError happen, kvm notifies user space to record the CPER,
> user space specifies and passes the contents of ESR_EL1 on taking
> a virtual SError interrupt to KVM, KVM enables virtual system
> error or asynchronous abort with this specifies syndrome. This
> patch modify the world-switch to restore VSESR_EL2, VSESR_EL2
> saves the virtual SError syndrome, it becomes the ESR_EL1 value when
> HCR_EL2.VSE injects an SError. This register is added by the
> RAS Extensions.

This commit message is confusing and doesn't help me understand the
patch.

I think this patch is trying to do too many things. I suggest you split
the patch into (at least) one patch that captures exception information
from the world-switch path, one patch that deals with the new exit
reason, and finally a patch with the new ioctl. That way you can write
a commit message for each patch describing first what the patch does,
and then why this is a good idea.

Neverthess, I added some random comments below.

>
> Changes since v3:
> (1) Move restore VSESR_EL2 value logic to a helper method
> (2) In the world-switch, not save VSESR_EL2, because no one cares the
> old VSESR_EL2 value
> (3) Add a new KVM_ARM_SEI ioctl to set the VSESR_EL2 value and pend
> a virtual system error
>
> Signed-off-by: Dongjiu Geng <gengdongjiu@huawei.com>
> Signed-off-by: Quanming Wu <wuquanming@huawei.com>
> ---
> Documentation/virtual/kvm/api.txt | 10 ++++++++++
> arch/arm/include/asm/kvm_host.h | 1 +
> arch/arm/kvm/arm.c | 7 +++++++
> arch/arm/kvm/guest.c | 5 +++++
> arch/arm64/include/asm/esr.h | 2 ++
> arch/arm64/include/asm/kvm_emulate.h | 10 ++++++++++
> arch/arm64/include/asm/kvm_host.h | 2 ++
> arch/arm64/include/asm/sysreg.h | 3 +++
> arch/arm64/kvm/guest.c | 14 ++++++++++++++
> arch/arm64/kvm/handle_exit.c | 25 +++++++++++++++++++------
> arch/arm64/kvm/hyp/switch.c | 14 ++++++++++++++
> include/uapi/linux/kvm.h | 8 ++++++++
> 12 files changed, 95 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index 3c248f7..852ac55 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -3377,6 +3377,16 @@ struct kvm_ppc_resize_hpt {
> __u32 pad;
> };
>
> +4.104 KVM_ARM_SEI
> +
> +Capability: KVM_EXIT_SERROR_INTR
> +Architectures: arm/arm64
> +Type: vcpu ioctl
> +Parameters: u64 (syndrome)
> +Returns: 0 in case of success
> +
> +Pend an virtual system error or asynchronous abort with user space specified.
> +

I don't understand enough about what this ioctl does by just reading
this text. Did you mean to say something like "Record that userspace
wishes to inject a pending virtual system error to the VCPU. Next time
the VCPU is run, th

> 5. The kvm_run structure
> ------------------------
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 31ee468..566292a 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -244,6 +244,7 @@ int kvm_arm_coproc_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *);
>
> int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
> int exception_index);
> +int kvm_vcpu_ioctl_sei(struct kvm_vcpu *vcpu, u64 *syndrome);
>
> static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
> unsigned long hyp_stack_ptr,
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 96dba7c..583294f 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -987,6 +987,13 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
> return -EFAULT;
> return kvm_arm_vcpu_has_attr(vcpu, &attr);
> }
> + case KVM_ARM_SEI: {
> + u64 syndrome;
> +
> + if (copy_from_user(&syndrome, argp, sizeof(syndrome)))
> + return -EFAULT;
> + return kvm_vcpu_ioctl_sei(vcpu, &syndrome);
> + }
> default:
> return -EINVAL;
> }
> diff --git a/arch/arm/kvm/guest.c b/arch/arm/kvm/guest.c
> index fa6182a..72505bf 100644
> --- a/arch/arm/kvm/guest.c
> +++ b/arch/arm/kvm/guest.c
> @@ -248,6 +248,11 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
> return -EINVAL;
> }
>
> +int kvm_vcpu_ioctl_sei(struct kvm_vcpu *vcpu, u64 *syndrome)
> +{
> + return 0;
> +}
> +
> int __attribute_const__ kvm_target_cpu(void)
> {
> switch (read_cpuid_part()) {
> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> index 22f9c90..d009c99 100644
> --- a/arch/arm64/include/asm/esr.h
> +++ b/arch/arm64/include/asm/esr.h
> @@ -127,6 +127,8 @@
> #define ESR_ELx_WFx_ISS_WFE (UL(1) << 0)
> #define ESR_ELx_xVC_IMM_MASK ((1UL << 16) - 1)
>
> +#define VSESR_ELx_IDS_ISS_MASK ((1UL << 25) - 1)
> +
> /* ESR value templates for specific events */
>
> /* BRK instruction trap from AArch64 state */
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 5f64ab2..93dc3d1 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -155,6 +155,16 @@ static inline u32 kvm_vcpu_get_hsr(const struct kvm_vcpu *vcpu)
> return vcpu->arch.fault.esr_el2;
> }
>
> +static inline u32 kvm_vcpu_get_vsesr(const struct kvm_vcpu *vcpu)
> +{
> + return vcpu->arch.fault.vsesr_el2;
> +}
> +
> +static inline void kvm_vcpu_set_vsesr(struct kvm_vcpu *vcpu, unsigned long val)
> +{
> + vcpu->arch.fault.vsesr_el2 = val;
> +}
> +
> static inline int kvm_vcpu_get_condition(const struct kvm_vcpu *vcpu)
> {
> u32 esr = kvm_vcpu_get_hsr(vcpu);
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index e7705e7..b6242fb 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -86,6 +86,7 @@ struct kvm_vcpu_fault_info {
> u32 esr_el2; /* Hyp Syndrom Register */
> u64 far_el2; /* Hyp Fault Address Register */
> u64 hpfar_el2; /* Hyp IPA Fault Address Register */
> + u32 vsesr_el2; /* Virtual SError Exception Syndrome Register */
> };
>
> /*
> @@ -385,6 +386,7 @@ int kvm_arm_vcpu_arch_get_attr(struct kvm_vcpu *vcpu,
> struct kvm_device_attr *attr);
> int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
> struct kvm_device_attr *attr);
> +int kvm_vcpu_ioctl_sei(struct kvm_vcpu *vcpu, u64 *syndrome);
>
> static inline void __cpu_init_stage2(void)
> {
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 32964c7..3af6907 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -125,6 +125,9 @@
> #define REG_PSTATE_PAN_IMM sys_reg(0, 0, 4, 0, 4)
> #define REG_PSTATE_UAO_IMM sys_reg(0, 0, 4, 0, 3)
>
> +/* virtual SError exception syndrome register in armv8.2 */
> +#define REG_VSESR_EL2 sys_reg(3, 4, 5, 2, 3)
> +
> #define SET_PSTATE_PAN(x) __emit_inst(0xd5000000 | REG_PSTATE_PAN_IMM | \
> (!!x)<<8 | 0x1f)
> #define SET_PSTATE_UAO(x) __emit_inst(0xd5000000 | REG_PSTATE_UAO_IMM | \
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index b37446a..21c20b0 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -277,6 +277,20 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
> return -EINVAL;
> }
>
> +int kvm_vcpu_ioctl_sei(struct kvm_vcpu *vcpu, u64 *syndrome)
> +{
> + u64 reg = *syndrome;
> +
> + if (cpus_have_const_cap(ARM64_HAS_RAS_EXTN) && reg)
> + /* set vsesr_el2[24:0] with value that user space specified */
> + kvm_vcpu_set_vsesr(vcpu, reg & VSESR_ELx_IDS_ISS_MASK);

Are you really supposed to fail silently here if trying to do this on a
system that doesn't have RAS ?

Why can you not set reg to 0 here? That doesn't seem to be documented
anywhere, and shouldn't the function return -EINVAL in this case?

Also, if you do this, but don't run the VCPU, then migrate the VM, and
run the VCPU on the new destination, isn't this information lost?

> +
> + /* inject virtual system Error or asynchronous abort */
> + kvm_inject_vabt(vcpu);
> +
> + return 0;
> +}
> +
> int __attribute_const__ kvm_target_cpu(void)
> {
> unsigned long implementor = read_cpuid_implementor();
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index c89d83a..23c02c2 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -180,7 +180,11 @@ static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
>
> static int kvm_handle_guest_sei(struct kvm_vcpu *vcpu, struct kvm_run *run)
> {
> - unsigned long fault_ipa = kvm_vcpu_get_fault_ipa(vcpu);
> + unsigned long hva, fault_ipa = kvm_vcpu_get_fault_ipa(vcpu);
> + struct kvm_memory_slot *memslot;
> + int hsr, ret = 1;
> + bool writable;
> + gfn_t gfn;
>
> if (handle_guest_sei((unsigned long)fault_ipa,
> kvm_vcpu_get_hsr(vcpu))) {
> @@ -190,9 +194,20 @@ static int kvm_handle_guest_sei(struct kvm_vcpu *vcpu, struct kvm_run *run)
> (unsigned long)kvm_vcpu_get_hsr(vcpu));
>
> kvm_inject_vabt(vcpu);
> + } else {
> + hsr = kvm_vcpu_get_hsr(vcpu);
> +
> + gfn = fault_ipa >> PAGE_SHIFT;
> + memslot = gfn_to_memslot(vcpu->kvm, gfn);
> + hva = gfn_to_hva_memslot_prot(memslot, gfn, &writable);
> +
> + run->exit_reason = KVM_EXIT_SERROR_INTR;
> + run->serror_intr.syndrome_info = hsr;
> + run->serror_intr.address = hva;
> + ret = 0;
> }
>
> - return 0;
> + return ret;
> }
>
> /*
> @@ -218,8 +233,7 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
> *vcpu_pc(vcpu) -= adj;
> }
>
> - kvm_handle_guest_sei(vcpu, run);
> - return 1;
> + return kvm_handle_guest_sei(vcpu, run);
> }
>
> exception_index = ARM_EXCEPTION_CODE(exception_index);
> @@ -228,8 +242,7 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
> case ARM_EXCEPTION_IRQ:
> return 1;
> case ARM_EXCEPTION_EL1_SERROR:
> - kvm_handle_guest_sei(vcpu, run);
> - return 1;
> + return kvm_handle_guest_sei(vcpu, run);
> case ARM_EXCEPTION_TRAP:
> /*
> * See ARM ARM B1.14.1: "Hyp traps on instructions
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index aede165..6d17c97 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -67,6 +67,13 @@ static hyp_alternate_select(__activate_traps_arch,
> __activate_traps_nvhe, __activate_traps_vhe,
> ARM64_HAS_VIRT_HOST_EXTN);
>
> +static void __hyp_text __sysreg_set_vsesr(struct kvm_vcpu *vcpu)
> +{
> + if (cpus_have_const_cap(ARM64_HAS_RAS_EXTN) &&
> + (vcpu->arch.hcr_el2 & HCR_VSE))
> + write_sysreg_s(vcpu->arch.fault.vsesr_el2, REG_VSESR_EL2);
> +}
> +
> static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
> {
> u64 val;
> @@ -86,6 +93,13 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
> isb();
> }
> write_sysreg(val, hcr_el2);
> +
> + /*
> + * If the virtual SError interrupt is taken to EL1 using AArch64,
> + * then VSESR_EL2 provides the syndrome value reported in ESR_EL1.
> + */
> + __sysreg_set_vsesr(vcpu);
> +
> /* Trap on AArch32 cp15 c15 accesses (EL1 or EL0) */
> write_sysreg(1 << 15, hstr_el2);
> /*
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 27fe556..ab91fe3 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -205,6 +205,7 @@ struct kvm_hyperv_exit {
> #define KVM_EXIT_S390_STSI 25
> #define KVM_EXIT_IOAPIC_EOI 26
> #define KVM_EXIT_HYPERV 27
> +#define KVM_EXIT_SERROR_INTR 28
>
> /* For KVM_EXIT_INTERNAL_ERROR */
> /* Emulate instruction failed. */
> @@ -360,6 +361,11 @@ struct kvm_run {
> struct {
> __u8 vector;
> } eoi;
> + /* KVM_EXIT_SERROR_INTR */
> + struct {
> + __u32 syndrome_info;
> + __u64 address;
> + } serror_intr;
> /* KVM_EXIT_HYPERV */
> struct kvm_hyperv_exit hyperv;
> /* Fix the size of the union. */
> @@ -1301,6 +1307,8 @@ struct kvm_s390_ucas_mapping {
> #define KVM_S390_GET_IRQ_STATE _IOW(KVMIO, 0xb6, struct kvm_s390_irq_state)
> /* Available with KVM_CAP_X86_SMM */
> #define KVM_SMI _IO(KVMIO, 0xb7)
> +/* Available with KVM_EXIT_SERROR_INTR */
> +#define KVM_ARM_SEI _IO(KVMIO, 0xb8)
>
> #define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
> #define KVM_DEV_ASSIGN_PCI_2_3 (1 << 1)
> --
> 2.10.1
>

Thanks,
-Christoffer