[PATCH v2 1/3] RISC-V: KVM: Implement kvm_arch_vcpu_ioctl_set_guest_debug()
Chao Du
duchao at eswincomputing.com
Thu Feb 29 23:27:18 PST 2024
On 2024-03-01 15:29, Anup Patel <anup at brainfault.org> wrote:
>
> On Fri, Mar 1, 2024 at 12:05 PM Chao Du <duchao at eswincomputing.com> wrote:
> >
> > On 2024-03-01 13:00, Anup Patel <anup at brainfault.org> wrote:
> > >
> > > On Fri, Mar 1, 2024 at 7:08 AM Chao Du <duchao at eswincomputing.com> wrote:
> > > >
> > > > kvm_vm_ioctl_check_extension(): Return 1 if KVM_CAP_SET_GUEST_DEBUG is
> > > > been checked.
> > > >
> > > > kvm_arch_vcpu_ioctl_set_guest_debug(): Update the guest_debug flags
> > > > from userspace accordingly. Route the breakpoint exceptions to HS mode
> > > > if the VCPU is being debugged by userspace, by clearing the
> > > > corresponding bit in hedeleg. Write the actual CSR in
> > > > kvm_arch_vcpu_load().
> > > >
> > > > Signed-off-by: Chao Du <duchao at eswincomputing.com>
> > > > ---
> > > > arch/riscv/include/asm/kvm_host.h | 17 +++++++++++++++++
> > > > arch/riscv/include/uapi/asm/kvm.h | 1 +
> > > > arch/riscv/kvm/main.c | 18 ++----------------
> > > > arch/riscv/kvm/vcpu.c | 15 +++++++++++++--
> > > > arch/riscv/kvm/vm.c | 1 +
> > > > 5 files changed, 34 insertions(+), 18 deletions(-)
> > > >
> > > > diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> > > > index 484d04a92fa6..9ee3f03ba5d1 100644
> > > > --- a/arch/riscv/include/asm/kvm_host.h
> > > > +++ b/arch/riscv/include/asm/kvm_host.h
> > > > @@ -43,6 +43,22 @@
> > > > KVM_ARCH_REQ_FLAGS(5, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> > > > #define KVM_REQ_STEAL_UPDATE KVM_ARCH_REQ(6)
> > > >
> > > > +#define KVM_HEDELEG_DEFAULT ((_AC(1, UL) << EXC_INST_MISALIGNED) | \
> > > > + (_AC(1, UL) << EXC_BREAKPOINT) | \
> > > > + (_AC(1, UL) << EXC_SYSCALL) | \
> > > > + (_AC(1, UL) << EXC_INST_PAGE_FAULT) | \
> > > > + (_AC(1, UL) << EXC_LOAD_PAGE_FAULT) | \
> > > > + (_AC(1, UL) << EXC_STORE_PAGE_FAULT))
> > >
> > > Use BIT(xyz) here. For example: BIT(EXC_INST_MISALIGNED)
> >
> > Thanks, I will use BIT() instead in next revision.
> >
> > >
> >
> > > Also, BIT(EXC_BREAKPOINT) should not be part of KVM_HEDELEG_DEFAULT.
> >
> > I think the bit EXC_BREAKPOINT should be set by default, like what you
> > already did in kvm_arch_hardware_enable(). Then the VS could get the ebreak
> > and handle it accordingly.
> >
> > If the guest_debug is enabled, ebreak instructions are inserted by the
> > userspace(QEMU). So KVM should 'intercept' the ebreak and exit to QEMU.
> > Bit EXC_BREAKPOINT should be cleared in this case.
>
> If EXC_BREAKPOINT is delegated by default then it is not consistent with
> vcpu->guest_debug which is not enabled by default.
To enable the guest_debug corresponding to NOT delegate the EXC_BREAKPOINT.
They are somehow 'opposite'.
This 'kvm_guest_debug' feature is different from "debug in the guest".
The later requires the delegation of EXC_BREAKPOINT.
The former does not.
>
> >
> > >
> > > > +#define KVM_HEDELEG_GUEST_DEBUG ((_AC(1, UL) << EXC_INST_MISALIGNED) | \
> > > > + (_AC(1, UL) << EXC_SYSCALL) | \
> > > > + (_AC(1, UL) << EXC_INST_PAGE_FAULT) | \
> > > > + (_AC(1, UL) << EXC_LOAD_PAGE_FAULT) | \
> > > > + (_AC(1, UL) << EXC_STORE_PAGE_FAULT))
> > >
> > > No need for KVM_HEDELEG_GUEST_DEBUG, see below.
> > >
> > > > +
> > > > +#define KVM_HIDELEG_DEFAULT ((_AC(1, UL) << IRQ_VS_SOFT) | \
> > > > + (_AC(1, UL) << IRQ_VS_TIMER) | \
> > > > + (_AC(1, UL) << IRQ_VS_EXT))
> > > > +
> > >
> > > Same as above, use BIT(xyz) here.
> > >
> > > > enum kvm_riscv_hfence_type {
> > > > KVM_RISCV_HFENCE_UNKNOWN = 0,
> > > > KVM_RISCV_HFENCE_GVMA_VMID_GPA,
> > > > @@ -169,6 +185,7 @@ struct kvm_vcpu_csr {
> > > > struct kvm_vcpu_config {
> > > > u64 henvcfg;
> > > > u64 hstateen0;
> > > > + unsigned long hedeleg;
> > > > };
> > > >
> > > > struct kvm_vcpu_smstateen_csr {
> > > > diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
> > > > index 7499e88a947c..39f4f4b9dede 100644
> > > > --- a/arch/riscv/include/uapi/asm/kvm.h
> > > > +++ b/arch/riscv/include/uapi/asm/kvm.h
> > > > @@ -17,6 +17,7 @@
> > > >
> > > > #define __KVM_HAVE_IRQ_LINE
> > > > #define __KVM_HAVE_READONLY_MEM
> > > > +#define __KVM_HAVE_GUEST_DEBUG
> > > >
> > > > #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
> > > >
> > > > diff --git a/arch/riscv/kvm/main.c b/arch/riscv/kvm/main.c
> > > > index 225a435d9c9a..bab2ec34cd87 100644
> > > > --- a/arch/riscv/kvm/main.c
> > > > +++ b/arch/riscv/kvm/main.c
> > > > @@ -22,22 +22,8 @@ long kvm_arch_dev_ioctl(struct file *filp,
> > > >
> > > > int kvm_arch_hardware_enable(void)
> > > > {
> > > > - unsigned long hideleg, hedeleg;
> > > > -
> > > > - hedeleg = 0;
> > > > - hedeleg |= (1UL << EXC_INST_MISALIGNED);
> > > > - hedeleg |= (1UL << EXC_BREAKPOINT);
> > > > - hedeleg |= (1UL << EXC_SYSCALL);
> > > > - hedeleg |= (1UL << EXC_INST_PAGE_FAULT);
> > > > - hedeleg |= (1UL << EXC_LOAD_PAGE_FAULT);
> > > > - hedeleg |= (1UL << EXC_STORE_PAGE_FAULT);
> > > > - csr_write(CSR_HEDELEG, hedeleg);
> > > > -
> > > > - hideleg = 0;
> > > > - hideleg |= (1UL << IRQ_VS_SOFT);
> > > > - hideleg |= (1UL << IRQ_VS_TIMER);
> > > > - hideleg |= (1UL << IRQ_VS_EXT);
> > > > - csr_write(CSR_HIDELEG, hideleg);
> > > > + csr_write(CSR_HEDELEG, KVM_HEDELEG_DEFAULT);
> > > > + csr_write(CSR_HIDELEG, KVM_HIDELEG_DEFAULT);
> > > >
> > > > /* VS should access only the time counter directly. Everything else should trap */
> > > > csr_write(CSR_HCOUNTEREN, 0x02);
> > > > diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
> > > > index b5ca9f2e98ac..242076c2227f 100644
> > > > --- a/arch/riscv/kvm/vcpu.c
> > > > +++ b/arch/riscv/kvm/vcpu.c
> > > > @@ -475,8 +475,15 @@ int kvm_arch_vcpu_ioctl_set_mpstate(struct kvm_vcpu *vcpu,
> > > > int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
> > > > struct kvm_guest_debug *dbg)
> > > > {
> > > > - /* TODO; To be implemented later. */
> > > > - return -EINVAL;
> > >
> > > if (vcpu->arch.ran_atleast_once)
> > > return -EBUSY;
> >
> > If we enabled the guest_debug in QEMU side, then the KVM_SET_GUEST_DEBUG ioctl
> > will come before the first KVM_RUN. This will always cause an ERROR.
>
> The check ensures that KVM user space can only enable/disable
> guest debug before the VCPU is run. I don't see why this would
> fail for QEMU.
In the current implementation of GDB and QEMU, the userspace will enable/disable
guest_debug frequently during the debugging (almost every step).
The sequence should like:
KVM_SET_GUEST_DEBUG enable
KVM_RUN
KVM_SET_GUEST_DEBUG disable
KVM_SET_GUEST_DEBUG enable
KVM_RUN
KVM_SET_GUEST_DEBUG disable
KVM_SET_GUEST_DEBUG enable
KVM_RUN
KVM_SET_GUEST_DEBUG disable
...
>
> >
> > >
> > >
> > > > + if (dbg->control & KVM_GUESTDBG_ENABLE) {
> > > > + vcpu->guest_debug = dbg->control;
> > > > + vcpu->arch.cfg.hedeleg = KVM_HEDELEG_GUEST_DEBUG;
> > > > + } else {
> > > > + vcpu->guest_debug = 0;
> > > > + vcpu->arch.cfg.hedeleg = KVM_HEDELEG_DEFAULT;
> > > > + }
> > >
> > > Don't update vcpu->arch.cfg.hedeleg here since it should be only done
> > > in kvm_riscv_vcpu_setup_config().
> > >
> > > > +
> > > > + return 0;
> > > > }
> > > >
> > > > static void kvm_riscv_vcpu_setup_config(struct kvm_vcpu *vcpu)
> > > > @@ -505,6 +512,9 @@ static void kvm_riscv_vcpu_setup_config(struct kvm_vcpu *vcpu)
> > > > if (riscv_isa_extension_available(isa, SMSTATEEN))
> > > > cfg->hstateen0 |= SMSTATEEN0_SSTATEEN0;
> > > > }
> > > > +
> > > > + if (!vcpu->guest_debug)
> > > > + cfg->hedeleg = KVM_HEDELEG_DEFAULT;
> > >
> > > This should be:
> > >
> > > cfg->hedeleg = KVM_HEDELEG_DEFAULT;
> > > if (vcpu->guest_debug)
> > > cfg->hedeleg |= BIT(EXC_BREAKPOINT);
> >
> > Like above, here the logic should be:
> >
> > cfg->hedeleg = KVM_HEDELEG_DEFAULT; // with BIT(EXC_BREAKPOINT)
> > if (vcpu->guest_debug)
> > cfg->hedeleg &= ~BIT(EXC_BREAKPOINT);
> >
> > Another approach is:
> > initialize the cfg->hedeleg as KVM_HEDELEG_DEFAULT during kvm_arch_vcpu_create().
> > Besides that, only update the cfg->hedeleg in kvm_arch_vcpu_ioctl_set_guest_debug().
>
> I disagree. We should handle hedeleg just like we handle henvcfg.
OK, let's only update the cfg->hedeleg in kvm_riscv_vcpu_setup_config().
>
> >
> > >
> > > > }
> > > >
> > > > void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> > > > @@ -519,6 +529,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> > > > csr_write(CSR_VSEPC, csr->vsepc);
> > > > csr_write(CSR_VSCAUSE, csr->vscause);
> > > > csr_write(CSR_VSTVAL, csr->vstval);
> > > > + csr_write(CSR_HEDELEG, cfg->hedeleg);
> > > > csr_write(CSR_HVIP, csr->hvip);
> > > > csr_write(CSR_VSATP, csr->vsatp);
> > > > csr_write(CSR_HENVCFG, cfg->henvcfg);
> > > > diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
> > > > index ce58bc48e5b8..7396b8654f45 100644
> > > > --- a/arch/riscv/kvm/vm.c
> > > > +++ b/arch/riscv/kvm/vm.c
> > > > @@ -186,6 +186,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> > > > case KVM_CAP_READONLY_MEM:
> > > > case KVM_CAP_MP_STATE:
> > > > case KVM_CAP_IMMEDIATE_EXIT:
> > > > + case KVM_CAP_SET_GUEST_DEBUG:
> > > > r = 1;
> > > > break;
> > > > case KVM_CAP_NR_VCPUS:
> > > > --
> > > > 2.17.1
> > > >
> > >
> > > Regards,
> > > Anup
> >
> > Thanks,
> > Chao
>
> Regards,
> Anup
Thanks,
Chao
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