Re: [PATCH] x86/vm_event: toggle singlestep from vm_event response

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 29/06/15 13:58, Tamas K Lengyel wrote:
> Add an option to the vm_event response to toggle singlestepping on the vCPU.
>
> Singed-off-by: Tamas K Lengyel <tlengyel@novetta.com>
> ---
>  MAINTAINERS                    |  1 +
>  xen/arch/x86/Makefile          |  1 +
>  xen/arch/x86/hvm/hvm.c         |  8 ++++++++
>  xen/arch/x86/vm_event.c        | 41 +++++++++++++++++++++++++++++++++++++++++
>  xen/common/vm_event.c          |  8 +++++++-
>  xen/include/asm-arm/vm_event.h | 29 +++++++++++++++++++++++++++++
>  xen/include/asm-x86/hvm/hvm.h  |  3 +++
>  xen/include/asm-x86/vm_event.h | 25 +++++++++++++++++++++++++
>  xen/include/public/vm_event.h  | 11 ++++++++---
>  9 files changed, 123 insertions(+), 4 deletions(-)
>  create mode 100644 xen/arch/x86/vm_event.c
>  create mode 100644 xen/include/asm-arm/vm_event.h
>  create mode 100644 xen/include/asm-x86/vm_event.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 6b1068e..59c0822 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -383,6 +383,7 @@ F:	xen/common/vm_event.c
>  F:	xen/common/mem_access.c
>  F:	xen/arch/x86/hvm/event.c
>  F:	xen/arch/x86/monitor.c
> +F:	xen/arch/x86/vm_event.c
>  
>  XENTRACE
>  M:	George Dunlap <george.dunlap@eu.citrix.com>
> diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
> index 37e547c..5f24951 100644
> --- a/xen/arch/x86/Makefile
> +++ b/xen/arch/x86/Makefile
> @@ -60,6 +60,7 @@ obj-y += machine_kexec.o
>  obj-y += crash.o
>  obj-y += tboot.o
>  obj-y += hpet.o
> +obj-y += vm_event.o
>  obj-y += xstate.o
>  
>  obj-$(crash_debug) += gdbstub.o
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 535d622..2bfd1b0 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -6431,6 +6431,14 @@ int hvm_debug_op(struct vcpu *v, int32_t op)
>      return rc;
>  }
>  
> +void hvm_toggle_singlestep(struct vcpu *v)
> +{
> +    if ( !cpu_has_monitor_trap_flag )

monitor_trap_flag is a VMX feature.  This will never be true on AMD
systems.  (its use in hvm_debug_op() is also dubious)

> +        return;
> +
> +    v->arch.hvm_vcpu.single_step = !v->arch.hvm_vcpu.single_step;
> +}
> +
>  int nhvm_vcpu_hostrestore(struct vcpu *v, struct cpu_user_regs *regs)
>  {
>      if (hvm_funcs.nhvm_vcpu_hostrestore)
> diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
> new file mode 100644
> index 0000000..95b30ad
> --- /dev/null
> +++ b/xen/arch/x86/vm_event.c
> @@ -0,0 +1,41 @@
> +/*
> + * arch/x86/vm_event.c
> + *
> + * Architecture-specific vm_event handling routines
> + *
> + * Copyright (c) 2015 Tamas K Lengyel (tamas@tklengyel.com)
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public
> + * License v2 as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public
> + * License along with this program; if not, write to the
> + * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
> + * Boston, MA 021110-1307, USA.
> + */
> +
> +#include <xen/sched.h>
> +#include <asm/hvm/hvm.h>
> +
> +void vm_event_toggle_singlestep(struct domain *d, struct vcpu *v)
> +{
> +    if ( (v == current) || !is_hvm_domain(d) )

Why is 'current' excluded?

> +        return;
> +
> +    hvm_toggle_singlestep(v);
> +}
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> diff --git a/xen/common/vm_event.c b/xen/common/vm_event.c
> index 120a78a..2ee27e2 100644
> --- a/xen/common/vm_event.c
> +++ b/xen/common/vm_event.c
> @@ -27,6 +27,7 @@
>  #include <xen/vm_event.h>
>  #include <xen/mem_access.h>
>  #include <asm/p2m.h>
> +#include <asm/vm_event.h>
>  #include <xsm/xsm.h>
>  
>  /* for public/io/ring.h macros */
> @@ -399,9 +400,14 @@ void vm_event_resume(struct domain *d, struct vm_event_domain *ved)
>  
>          };
>  
> -        /* Unpause domain. */
>          if ( rsp.flags & VM_EVENT_FLAG_VCPU_PAUSED )
> +        {
> +            if ( rsp.flags & VM_EVENT_FLAG_TOGGLE_SINGLESTEP )
> +                vm_event_toggle_singlestep(d, v);
> +
> +            /* Unpause domain. */

I don't think this comment is useful to keep.

>              vm_event_vcpu_unpause(v);
> +        }
>      }
>  }
>  
> diff --git a/xen/include/asm-arm/vm_event.h b/xen/include/asm-arm/vm_event.h
> new file mode 100644
> index 0000000..a4cf4c6
> --- /dev/null
> +++ b/xen/include/asm-arm/vm_event.h
> @@ -0,0 +1,29 @@
> +/*
> + * vm_event.h: architecture specific vm_event handling routines
> + *
> + * Copyright (c) 2015 Tamas K Lengyel (tamas@tklengyel.com)
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along with
> + * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
> + * Place - Suite 330, Boston, MA 02111-1307 USA.
> + */
> +
> +#ifndef __ASM_ARM_VM_EVENT_H__
> +#define __ASM_ARM_VM_EVENT_H__
> +
> +static inline
> +void vm_event_toggle_singlestep(struct domain *d, struct vcpu *v)
> +{
> +    /* Not supported on ARM. */
> +}
> +
> +#endif /* __ASM_ARM_VM_EVENT_H__ */
> diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
> index 57f9605..073b758 100644
> --- a/xen/include/asm-x86/hvm/hvm.h
> +++ b/xen/include/asm-x86/hvm/hvm.h
> @@ -448,6 +448,9 @@ static inline void hvm_set_info_guest(struct vcpu *v)
>  
>  int hvm_debug_op(struct vcpu *v, int32_t op);
>  
> +/* Caller should pause vcpu before calling this function */
> +void hvm_toggle_singlestep(struct vcpu *v);
> +
>  static inline void hvm_invalidate_regs_fields(struct cpu_user_regs *regs)
>  {
>  #ifndef NDEBUG
> diff --git a/xen/include/asm-x86/vm_event.h b/xen/include/asm-x86/vm_event.h
> new file mode 100644
> index 0000000..d36dd50
> --- /dev/null
> +++ b/xen/include/asm-x86/vm_event.h
> @@ -0,0 +1,25 @@
> +/*
> + * vm_event.h: architecture specific vm_event handling routines
> + *
> + * Copyright (c) 2015 Tamas K Lengyel (tamas@tklengyel.com)
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms and conditions of the GNU General Public License,
> + * version 2, as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along with
> + * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
> + * Place - Suite 330, Boston, MA 02111-1307 USA.
> + */
> +
> +#ifndef __ASM_X86_VM_EVENT_H__
> +#define __ASM_X86_VM_EVENT_H__
> +

This should either include sched.h or pre-declare struct domain and vcpu.

Otherwise, including <asm/vm_event.h> first in a list of includes will
cause a compile error.

~Andrew

> +void vm_event_toggle_singlestep(struct domain *d, struct vcpu *v);
> +
> +#endif /* __ASM_X86_VM_EVENT_H__ */
> diff --git a/xen/include/public/vm_event.h b/xen/include/public/vm_event.h
> index 577e971..6156d9e 100644
> --- a/xen/include/public/vm_event.h
> +++ b/xen/include/public/vm_event.h
> @@ -44,9 +44,14 @@
>   *  paused
>   * VCPU_PAUSED in a response signals to unpause the vCPU
>   */
> -#define VM_EVENT_FLAG_VCPU_PAUSED     (1 << 0)
> -/* Flags to aid debugging mem_event */
> -#define VM_EVENT_FLAG_FOREIGN         (1 << 1)
> +#define VM_EVENT_FLAG_VCPU_PAUSED       (1 << 0)
> +/* Flag to aid debugging mem_event */
> +#define VM_EVENT_FLAG_FOREIGN           (1 << 1)
> +/*
> + * Toggle singlestepping on vm_event response.
> + * Requires the vCPU to be paused already (synchronous events only).
> + */
> +#define VM_EVENT_FLAG_TOGGLE_SINGLESTEP (1 << 2)
>  
>  /*
>   * Reasons for the vm event request