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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v4] x86/monitor: Notify monitor if an emulation fails.
On Wed, Jul 12, 2017 at 11:21 AM, Petre Pircalabu
<ppircalabu@xxxxxxxxxxxxxxx> wrote:
> If case of a vm_event with the emulate_flags set, if the instruction
> cannot be emulated, the monitor should be notified instead of directly
> injecting a hw exception.
> This behavior can be used to re-execute an instruction not supported by
> the emulator using the real processor (e.g. altp2m) instead of just
> crashing.
>
> Signed-off-by: Petre Pircalabu <ppircalabu@xxxxxxxxxxxxxxx>
>
> ---
> Changed since v1:
> * Removed the emulation kind check when calling hvm_inject_hw_exception
>
> Changed since v2:
> * Removed a file added by mistake
>
> Changed since v3:
> * Removed extra stray line
> * Added the _enabled suffix to the emul_unhandleable monitor option
> ---
> tools/libxc/include/xenctrl.h | 2 ++
> tools/libxc/xc_monitor.c | 14 ++++++++++++++
> xen/arch/x86/hvm/emulate.c | 5 ++++-
> xen/arch/x86/hvm/monitor.c | 18 ++++++++++++++++++
> xen/arch/x86/monitor.c | 12 ++++++++++++
> xen/include/asm-x86/domain.h | 1 +
> xen/include/asm-x86/hvm/monitor.h | 1 +
> xen/include/asm-x86/monitor.h | 3 ++-
> xen/include/public/domctl.h | 1 +
> xen/include/public/vm_event.h | 2 ++
> 10 files changed, 57 insertions(+), 2 deletions(-)
>
> diff --git a/tools/libxc/include/xenctrl.h b/tools/libxc/include/xenctrl.h
> index c51bb3b..8deb5ac 100644
> --- a/tools/libxc/include/xenctrl.h
> +++ b/tools/libxc/include/xenctrl.h
> @@ -2029,6 +2029,8 @@ int xc_monitor_debug_exceptions(xc_interface *xch,
> domid_t domain_id,
> int xc_monitor_cpuid(xc_interface *xch, domid_t domain_id, bool enable);
> int xc_monitor_privileged_call(xc_interface *xch, domid_t domain_id,
> bool enable);
> +int xc_monitor_emul_unhandleable(xc_interface *xch, domid_t domain_id,
> + bool enable);
> /**
> * This function enables / disables emulation for each REP for a
> * REP-compatible instruction.
> diff --git a/tools/libxc/xc_monitor.c b/tools/libxc/xc_monitor.c
> index b44ce93..8e72c6c 100644
> --- a/tools/libxc/xc_monitor.c
> +++ b/tools/libxc/xc_monitor.c
> @@ -216,6 +216,20 @@ int xc_monitor_privileged_call(xc_interface *xch,
> domid_t domain_id,
> return do_domctl(xch, &domctl);
> }
>
> +int xc_monitor_emul_unhandleable(xc_interface *xch, domid_t domain_id,
> + bool enable)
> +{
> + DECLARE_DOMCTL;
> +
> + domctl.cmd = XEN_DOMCTL_monitor_op;
> + domctl.domain = domain_id;
> + domctl.u.monitor_op.op = enable ? XEN_DOMCTL_MONITOR_OP_ENABLE
> + : XEN_DOMCTL_MONITOR_OP_DISABLE;
> + domctl.u.monitor_op.event = XEN_DOMCTL_MONITOR_EVENT_EMUL_UNHANDLEABLE;
> +
> + return do_domctl(xch, &domctl);
> +}
> +
> /*
> * Local variables:
> * mode: C
> diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
> index e97aa69..f52aa87 100644
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -14,12 +14,14 @@
> #include <xen/sched.h>
> #include <xen/paging.h>
> #include <xen/trace.h>
> +#include <xen/vm_event.h>
> #include <asm/event.h>
> #include <asm/i387.h>
> #include <asm/xstate.h>
> #include <asm/hvm/emulate.h>
> #include <asm/hvm/hvm.h>
> #include <asm/hvm/ioreq.h>
> +#include <asm/hvm/monitor.h>
> #include <asm/hvm/trace.h>
> #include <asm/hvm/support.h>
> #include <asm/hvm/svm/svm.h>
> @@ -2101,7 +2103,8 @@ void hvm_emulate_one_vm_event(enum emul_kind kind,
> unsigned int trapnr,
> return;
> case X86EMUL_UNHANDLEABLE:
> hvm_dump_emulation_state(XENLOG_G_DEBUG, "Mem event", &ctx);
> - hvm_inject_hw_exception(trapnr, errcode);
> + if ( !hvm_monitor_emul_unhandleable() )
> + hvm_inject_hw_exception(trapnr, errcode);
> break;
> case X86EMUL_EXCEPTION:
> hvm_inject_event(&ctx.ctxt.event);
> diff --git a/xen/arch/x86/hvm/monitor.c b/xen/arch/x86/hvm/monitor.c
> index a7ccfc4..977a96b 100644
> --- a/xen/arch/x86/hvm/monitor.c
> +++ b/xen/arch/x86/hvm/monitor.c
> @@ -57,6 +57,24 @@ bool_t hvm_monitor_cr(unsigned int index, unsigned long
> value, unsigned long old
> return 0;
> }
>
> +bool hvm_monitor_emul_unhandleable(void)
> +{
> + struct vcpu *curr = current;
> + struct domain *d = curr->domain;
> +
> + /*
> + * Send a vm_event to the monitor to signal that the current
> + * instruction couldn't be emulated.
> + */
> + vm_event_request_t req = {
> + .reason = VM_EVENT_REASON_EMUL_UNHANDLEABLE,
> + .vcpu_id = curr->vcpu_id,
> + };
> +
> + return ( d->arch.monitor.emul_unhandleable_enabled &&
> + monitor_traps(curr, true, &req) );
So what happens if monitor_traps fails and returns -1? Since this gets
treated as a boolean, we will return true here and just silently
swallow the problem and likely make the VM hang in a loop. I think it
would be appropriate to crash the vm here if we can't emulate and also
can't notify the listener.
> +}
> +
> void hvm_monitor_msr(unsigned int msr, uint64_t value)
> {
> struct vcpu *curr = current;
> diff --git a/xen/arch/x86/monitor.c b/xen/arch/x86/monitor.c
> index 706454f..f791372 100644
> --- a/xen/arch/x86/monitor.c
> +++ b/xen/arch/x86/monitor.c
> @@ -283,6 +283,18 @@ int arch_monitor_domctl_event(struct domain *d,
> break;
> }
>
> + case XEN_DOMCTL_MONITOR_EVENT_EMUL_UNHANDLEABLE:
> + {
> + bool old_status = ad->monitor.emul_unhandleable_enabled;
> + if ( unlikely(old_status == requested_status) )
> + return -EEXIST;
> +
> + domain_pause(d);
> + ad->monitor.emul_unhandleable_enabled = requested_status;
> + domain_unpause(d);
> + break;
> + }
> +
> default:
> /*
> * Should not be reached unless arch_monitor_get_capabilities() is
> diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
> index c10522b..ae2d04d 100644
> --- a/xen/include/asm-x86/domain.h
> +++ b/xen/include/asm-x86/domain.h
> @@ -405,6 +405,7 @@ struct arch_domain
> unsigned int debug_exception_sync : 1;
> unsigned int cpuid_enabled : 1;
> unsigned int descriptor_access_enabled : 1;
> + unsigned int emul_unhandleable_enabled : 1;
> struct monitor_msr_bitmap *msr_bitmap;
> uint64_t write_ctrlreg_mask[4];
> } monitor;
> diff --git a/xen/include/asm-x86/hvm/monitor.h
> b/xen/include/asm-x86/hvm/monitor.h
> index d9efb35..4030be7 100644
> --- a/xen/include/asm-x86/hvm/monitor.h
> +++ b/xen/include/asm-x86/hvm/monitor.h
> @@ -47,6 +47,7 @@ int hvm_monitor_cpuid(unsigned long insn_length, unsigned
> int leaf,
> unsigned int subleaf);
> void hvm_monitor_interrupt(unsigned int vector, unsigned int type,
> unsigned int err, uint64_t cr2);
> +bool hvm_monitor_emul_unhandleable(void);
>
> #endif /* __ASM_X86_HVM_MONITOR_H__ */
>
> diff --git a/xen/include/asm-x86/monitor.h b/xen/include/asm-x86/monitor.h
> index c5c323b..38ba0ff 100644
> --- a/xen/include/asm-x86/monitor.h
> +++ b/xen/include/asm-x86/monitor.h
> @@ -77,7 +77,8 @@ static inline uint32_t arch_monitor_get_capabilities(struct
> domain *d)
> (1U << XEN_DOMCTL_MONITOR_EVENT_GUEST_REQUEST) |
> (1U << XEN_DOMCTL_MONITOR_EVENT_DEBUG_EXCEPTION) |
> (1U << XEN_DOMCTL_MONITOR_EVENT_CPUID) |
> - (1U << XEN_DOMCTL_MONITOR_EVENT_INTERRUPT);
> + (1U << XEN_DOMCTL_MONITOR_EVENT_INTERRUPT) |
> + (1U << XEN_DOMCTL_MONITOR_EVENT_EMUL_UNHANDLEABLE);
>
> /* Since we know this is on VMX, we can just call the hvm func */
> if ( hvm_is_singlestep_supported() )
> diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
> index ff39762..6bd8666 100644
> --- a/xen/include/public/domctl.h
> +++ b/xen/include/public/domctl.h
> @@ -1083,6 +1083,7 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_psr_cmt_op_t);
> #define XEN_DOMCTL_MONITOR_EVENT_PRIVILEGED_CALL 7
> #define XEN_DOMCTL_MONITOR_EVENT_INTERRUPT 8
> #define XEN_DOMCTL_MONITOR_EVENT_DESC_ACCESS 9
> +#define XEN_DOMCTL_MONITOR_EVENT_EMUL_UNHANDLEABLE 10
>
> struct xen_domctl_monitor_op {
> uint32_t op; /* XEN_DOMCTL_MONITOR_OP_* */
> diff --git a/xen/include/public/vm_event.h b/xen/include/public/vm_event.h
> index f01e471..5548afb 100644
> --- a/xen/include/public/vm_event.h
> +++ b/xen/include/public/vm_event.h
> @@ -148,6 +148,8 @@
> #define VM_EVENT_REASON_INTERRUPT 12
> /* A descriptor table register was accessed. */
> #define VM_EVENT_REASON_DESCRIPTOR_ACCESS 13
> +/* Current instruction couldn't be emulated */
> +#define VM_EVENT_REASON_EMUL_UNHANDLEABLE 14
>
> /* Supported values for the vm_event_write_ctrlreg index. */
> #define VM_EVENT_X86_CR0 0
> --
> 2.7.4
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