From: "Jan Beulich" <JBeulich@suse.com>
To: Tamas K Lengyel <tamas.lengyel@zentific.com>
Cc: Kevin Tian <kevin.tian@intel.com>,
Stefano Stabellini <sstabellini@kernel.org>,
George Dunlap <george.dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Julien Grall <julien.grall@arm.com>,
Paul Durrant <paul.durrant@citrix.com>,
Jun Nakajima <jun.nakajima@intel.com>,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH v4] x86/vm_event: Allow overwriting Xen's i-cache used for emulation
Date: Mon, 26 Sep 2016 04:33:01 -0600 [thread overview]
Message-ID: <57E9157D02000078001125EB@prv-mh.provo.novell.com> (raw)
In-Reply-To: <20160922185420.6100-1-tamas.lengyel@zentific.com>
>>> On 22.09.16 at 20:54, <tamas.lengyel@zentific.com> wrote:
> When emulating instructions Xen's emulator maintains a small i-cache fetched
> from the guest memory. This patch extends the vm_event interface to allow
> overwriting this i-cache via a buffer returned in the vm_event response.
>
> When responding to a SOFTWARE_BREAKPOINT event (INT3) the monitor subscriber
> normally has to remove the INT3 from memory - singlestep - place back INT3
> to allow the guest to continue execution. This routine however is
> susceptible
> to a race-condition on multi-vCPU guests. By allowing the subscriber to return
> the i-cache to be used for emulation it can side-step the problem by returning
> a clean buffer without the INT3 present.
>
> As part of this patch we rename hvm_mem_access_emulate_one to
> hvm_emulate_one_vm_event to better reflect that it is used in various
> vm_event
> scenarios now, not just in response to mem_access events.
>
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>
> Acked-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Non-VM-event specific code:
Reviewed-by: Jan Beulich <jbeulich@suse.com>
One question though:
> --- a/xen/arch/x86/vm_event.c
> +++ b/xen/arch/x86/vm_event.c
> @@ -209,11 +209,20 @@ void vm_event_emulate_check(struct vcpu *v, vm_event_response_t *rsp)
> if ( p2m_mem_access_emulate_check(v, rsp) )
> {
> if ( rsp->flags & VM_EVENT_FLAG_SET_EMUL_READ_DATA )
> - v->arch.vm_event->emul_read_data = rsp->data.emul_read_data;
> + v->arch.vm_event->emul.read = rsp->data.emul.read;
>
> v->arch.vm_event->emulate_flags = rsp->flags;
> }
> break;
> +
> + case VM_EVENT_REASON_SOFTWARE_BREAKPOINT:
> + if ( rsp->flags & VM_EVENT_FLAG_SET_EMUL_INSN_DATA )
> + {
> + v->arch.vm_event->emul.insn = rsp->data.emul.insn;
> + v->arch.vm_event->emulate_flags = rsp->flags;
> + }
> + break;
Is this intentionally different from the case above (where the setting
of ->emulate_flags is outside the inner if()?
Jan
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next prev parent reply other threads:[~2016-09-26 10:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-22 18:54 [PATCH v4] x86/vm_event: Allow overwriting Xen's i-cache used for emulation Tamas K Lengyel
2016-09-26 10:33 ` Jan Beulich [this message]
2016-09-26 14:30 ` Razvan Cojocaru
2016-09-26 14:55 ` Tamas K Lengyel
2016-09-26 15:26 ` Razvan Cojocaru
2016-09-26 15:54 ` Paul Durrant
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