Re: [PATCH 2/4] KVM: riscv: selftests: Add exception handling support
From: Haibo Xu
Date: Tue Aug 01 2023 - 21:46:59 EST
On Fri, Jul 28, 2023 at 5:37 PM Andrew Jones <ajones@xxxxxxxxxxxxxxxx> wrote:
>
> On Thu, Jul 27, 2023 at 03:20:06PM +0800, Haibo Xu wrote:
> > Add the infrastructure for exception handling in riscv selftests.
> > Currently, the guest_unexp_trap handler was used by default, which
> > aborts the test. Customized handlers can be enabled by calling
> > vm_install_exception_handler(vector) or vm_install_interrupt_handler().
> >
> > The code is inspired from that of x86/arm64.
> >
> > Signed-off-by: Haibo Xu <haibo1.xu@xxxxxxxxx>
> > ---
> > tools/testing/selftests/kvm/Makefile | 1 +
> > .../selftests/kvm/include/riscv/processor.h | 49 +++++++++
> > .../selftests/kvm/lib/riscv/handlers.S | 101 ++++++++++++++++++
> > .../selftests/kvm/lib/riscv/processor.c | 57 ++++++++++
> > 4 files changed, 208 insertions(+)
> > create mode 100644 tools/testing/selftests/kvm/lib/riscv/handlers.S
> >
> > diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> > index c692cc86e7da..70f3a5ba991e 100644
> > --- a/tools/testing/selftests/kvm/Makefile
> > +++ b/tools/testing/selftests/kvm/Makefile
> > @@ -52,6 +52,7 @@ LIBKVM_s390x += lib/s390x/diag318_test_handler.c
> > LIBKVM_s390x += lib/s390x/processor.c
> > LIBKVM_s390x += lib/s390x/ucall.c
> >
> > +LIBKVM_riscv += lib/riscv/handlers.S
> > LIBKVM_riscv += lib/riscv/processor.c
> > LIBKVM_riscv += lib/riscv/ucall.c
> >
> > diff --git a/tools/testing/selftests/kvm/include/riscv/processor.h b/tools/testing/selftests/kvm/include/riscv/processor.h
> > index d00d213c3805..9ea6e7bedc61 100644
> > --- a/tools/testing/selftests/kvm/include/riscv/processor.h
> > +++ b/tools/testing/selftests/kvm/include/riscv/processor.h
> > @@ -9,6 +9,7 @@
> >
> > #include "kvm_util.h"
> > #include <linux/stringify.h>
> > +#include <asm/csr.h>
> >
> > static inline uint64_t __kvm_reg_id(uint64_t type, uint64_t idx,
> > uint64_t size)
> > @@ -38,6 +39,54 @@ static inline uint64_t __kvm_reg_id(uint64_t type, uint64_t idx,
> > KVM_REG_RISCV_TIMER_REG(name), \
> > KVM_REG_SIZE_U64)
> >
> > +struct ex_regs {
> > + unsigned long ra;
> > + unsigned long sp;
> > + unsigned long gp;
> > + unsigned long tp;
> > + unsigned long t0;
> > + unsigned long t1;
> > + unsigned long t2;
> > + unsigned long s0;
> > + unsigned long s1;
> > + unsigned long a0;
> > + unsigned long a1;
> > + unsigned long a2;
> > + unsigned long a3;
> > + unsigned long a4;
> > + unsigned long a5;
> > + unsigned long a6;
> > + unsigned long a7;
> > + unsigned long s2;
> > + unsigned long s3;
> > + unsigned long s4;
> > + unsigned long s5;
> > + unsigned long s6;
> > + unsigned long s7;
> > + unsigned long s8;
> > + unsigned long s9;
> > + unsigned long s10;
> > + unsigned long s11;
> > + unsigned long t3;
> > + unsigned long t4;
> > + unsigned long t5;
> > + unsigned long t6;
> > + unsigned long epc;
> > + unsigned long status;
> > + unsigned long cause;
> > +};
> > +
> > +#define VECTOR_NUM 2
> > +#define EC_NUM 32
> > +#define EC_MASK (EC_NUM - 1)
>
> nit: My personal preference is to use something like NR_VECTORS and
> NR_EXCEPTIONS for these, since *_NUM type names are ambiguous with
> named indices.
>
> > +
> > +void vm_init_trap_vector_tables(struct kvm_vm *vm);
> > +void vcpu_init_trap_vector_tables(struct kvm_vcpu *vcpu);
>
> I think we should use a common name for these prototypes that the other
> architectures agree to and then put them in a common header. My vote for
> the naming is,
>
> void vm_init_vector_tables(struct kvm_vm *vm);
> void vcpu_init_vector_tables(struct kvm_vcpu *vcpu);
>
> > +
> > +typedef void(*handler_fn)(struct ex_regs *);
> > +void vm_install_exception_handler(struct kvm_vm *vm, int ec, handler_fn handler);
>
> I'd also put this typedef and prototype in a common header
> (with s/ec/vector/ to what you have here)
>
> > +void vm_install_interrupt_handler(struct kvm_vm *vm, handler_fn handler);
>
> I guess this one can stay risc-v specific for now since no other arch is
> using it.
>
> > +
> > /* L3 index Bit[47:39] */
> > #define PGTBL_L3_INDEX_MASK 0x0000FF8000000000ULL
> > #define PGTBL_L3_INDEX_SHIFT 39
> > diff --git a/tools/testing/selftests/kvm/lib/riscv/handlers.S b/tools/testing/selftests/kvm/lib/riscv/handlers.S
> > new file mode 100644
> > index 000000000000..ce0b1d5415b9
> > --- /dev/null
> > +++ b/tools/testing/selftests/kvm/lib/riscv/handlers.S
> > @@ -0,0 +1,101 @@
> > +// SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (c) 2023 Intel Corporation
> > + */
> > +
> > +#include <asm/csr.h>
>
> General note for all the asm below, please format with the first operand
> aligned, so
>
> <tab>op<tab>operand1, operand2, ...
>
> > +
> > +.macro save_context
> > + addi sp, sp, (-8*34)
> > +
> > + sd x1, 0(sp)
> > + sd x2, 8(sp)
> > + sd x3, 16(sp)
> > + sd x4, 24(sp)
> > + sd x5, 32(sp)
> > + sd x6, 40(sp)
> > + sd x7, 48(sp)
> > + sd x8, 56(sp)
> > + sd x9, 64(sp)
> > + sd x10, 72(sp)
> > + sd x11, 80(sp)
> > + sd x12, 88(sp)
> > + sd x13, 96(sp)
> > + sd x14, 104(sp)
> > + sd x15, 112(sp)
> > + sd x16, 120(sp)
> > + sd x17, 128(sp)
> > + sd x18, 136(sp)
> > + sd x19, 144(sp)
> > + sd x20, 152(sp)
> > + sd x21, 160(sp)
> > + sd x22, 168(sp)
> > + sd x23, 176(sp)
> > + sd x24, 184(sp)
> > + sd x25, 192(sp)
> > + sd x26, 200(sp)
> > + sd x27, 208(sp)
> > + sd x28, 216(sp)
> > + sd x29, 224(sp)
> > + sd x30, 232(sp)
> > + sd x31, 240(sp)
> > +
> > + csrr s0, CSR_SEPC
> > + csrr s1, CSR_SSTATUS
> > + csrr s2, CSR_SCAUSE
> > + sd s0, 248(sp)
> > + sd s1, 256(sp)
> > + sd s2, 264(sp)
> > +.endm
>
> Let's create a restore_context macro too in order to maintain balance.
>
> > +
> > +.balign 4
> > +.global exception_vectors
> > +exception_vectors:
> > + save_context
> > + move a0, sp
> > + la ra, ret_from_exception
> > + tail route_exception
> > +
> > +.global ret_from_exception
> > +ret_from_exception:
> > + ld s2, 264(sp)
> > + ld s1, 256(sp)
> > + ld s0, 248(sp)
> > + csrw CSR_SCAUSE, s2
> > + csrw CSR_SSTATUS, s1
> > + csrw CSR_SEPC, s0
> > +
> > + ld x31, 240(sp)
> > + ld x30, 232(sp)
> > + ld x29, 224(sp)
> > + ld x28, 216(sp)
> > + ld x27, 208(sp)
> > + ld x26, 200(sp)
> > + ld x25, 192(sp)
> > + ld x24, 184(sp)
> > + ld x23, 176(sp)
> > + ld x22, 168(sp)
> > + ld x21, 160(sp)
> > + ld x20, 152(sp)
> > + ld x19, 144(sp)
> > + ld x18, 136(sp)
> > + ld x17, 128(sp)
> > + ld x16, 120(sp)
> > + ld x15, 112(sp)
> > + ld x14, 104(sp)
> > + ld x13, 96(sp)
> > + ld x12, 88(sp)
> > + ld x11, 80(sp)
> > + ld x10, 72(sp)
> > + ld x9, 64(sp)
> > + ld x8, 56(sp)
> > + ld x7, 48(sp)
> > + ld x6, 40(sp)
> > + ld x5, 32(sp)
> > + ld x4, 24(sp)
> > + ld x3, 16(sp)
> > + ld x2, 8(sp)
> > + ld x1, 0(sp)
> > +
> > + addi sp, sp, (8*34)
> > + sret
> > diff --git a/tools/testing/selftests/kvm/lib/riscv/processor.c b/tools/testing/selftests/kvm/lib/riscv/processor.c
> > index d146ca71e0c0..f1b0be58a5dc 100644
> > --- a/tools/testing/selftests/kvm/lib/riscv/processor.c
> > +++ b/tools/testing/selftests/kvm/lib/riscv/processor.c
> > @@ -13,6 +13,8 @@
> >
> > #define DEFAULT_RISCV_GUEST_STACK_VADDR_MIN 0xac0000
> >
> > +static vm_vaddr_t exception_handlers;
> > +
> > static uint64_t page_align(struct kvm_vm *vm, uint64_t v)
> > {
> > return (v + vm->page_size) & ~(vm->page_size - 1);
> > @@ -367,3 +369,58 @@ void vcpu_args_set(struct kvm_vcpu *vcpu, unsigned int num, ...)
> > void assert_on_unhandled_exception(struct kvm_vcpu *vcpu)
> > {
> > }
> > +
> > +struct handlers {
> > + handler_fn exception_handlers[VECTOR_NUM][EC_NUM];
> > +};
> > +
> > +void route_exception(struct ex_regs *regs)
> > +{
> > + struct handlers *handlers = (struct handlers *)exception_handlers;
> > + int vector = 0, ec;
> > +
> > + ec = regs->cause & ~CAUSE_IRQ_FLAG;
> > + if (ec >= EC_NUM)
> > + goto guest_unexpected_trap;
> > +
> > + /* Use the same handler for all the interrupts */
> > + if (regs->cause & CAUSE_IRQ_FLAG) {
> > + vector = 1;
> > + ec = 0;
> > + }
> > +
> > + if (handlers && handlers->exception_handlers[vector][ec])
> > + return handlers->exception_handlers[vector][ec](regs);
> > +
> > +guest_unexpected_trap:
> > + return guest_unexp_trap();
>
> I think we want this to have consistent behavior with the other
> architectures, so we should be issuing a UCALL_UNHANDLED.
>
> > +}
> > +
> > +void vcpu_init_trap_vector_tables(struct kvm_vcpu *vcpu)
> > +{
> > + extern char exception_vectors;
> > +
> > + vcpu_set_reg(vcpu, RISCV_CSR_REG(stvec), (unsigned long)&exception_vectors);
> > +}
> > +
> > +void vm_init_trap_vector_tables(struct kvm_vm *vm)
> > +{
> > + vm->handlers = __vm_vaddr_alloc(vm, sizeof(struct handlers),
> > + vm->page_size, MEM_REGION_DATA);
> > +
> > + *(vm_vaddr_t *)addr_gva2hva(vm, (vm_vaddr_t)(&exception_handlers)) = vm->handlers;
> > +}
> > +
> > +void vm_install_exception_handler(struct kvm_vm *vm, int ec, void (*handler)(struct ex_regs *))
> > +{
> > + struct handlers *handlers = addr_gva2hva(vm, vm->handlers);
> > +
>
> Add assert here that ec is valid.
>
> > + handlers->exception_handlers[0][ec] = handler;
> > +}
> > +
> > +void vm_install_interrupt_handler(struct kvm_vm *vm, void (*handler)(struct ex_regs *))
> > +{
> > + struct handlers *handlers = addr_gva2hva(vm, vm->handlers);
> > +
> > + handlers->exception_handlers[1][0] = handler;
> > +}
> > --
> > 2.34.1
> >
>
> Besides some nits and wanting to get more consistency with the other
> architectures, this looks good to me.
>
Thanks for the review! Will fix them in v2.
> Thanks,
> drew