From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: Foreign VCPU register change? Date: Thu, 23 Aug 2012 18:49:46 +0100 Message-ID: References: Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============0629132727862884477==" Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Cutter 409 , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org > This message is in MIME format. Since your mail reader does not understand this format, some or all of this message may not be legible. --===============0629132727862884477== Content-type: multipart/alternative; boundary="B_3428592590_124082462" > This message is in MIME format. Since your mail reader does not understand this format, some or all of this message may not be legible. --B_3428592590_124082462 Content-type: text/plain; charset="ISO-8859-1" Content-transfer-encoding: quoted-printable FWIW I would expect your approach to basically work. Except... Does your domctl do a vcpu_pause()/vcpu_unpause() on the vcpu? This will ensure that the vcpu is both fully de-scheduled, and all of its register state is synced back into its vcpu structure. Otherwise you race the vcpu_sleep_nosync() -- and that=B9s assuming you also have a reason for that vcpu to sleep (e.g., non-zero pause counter), else vcpu_sleep_*() operations do nothing! In short, your problems are almost certainly something to do with the subtleties of actually putting a vcpu properly to sleep. -- Keir On 23/08/2012 18:37, "Cutter 409" wrote: > I'm making the register change directly from the hypervisor, inside of th= e > domctl code.=20 >=20 > It's a custom domctl that I've added. I'll look into what setcontext does > after it modifies the register values, though. >=20 > Thank you! >=20 > On Thu, Aug 23, 2012 at 1:34 PM, Keir Fraser wrote: >> On 23/08/2012 18:25, "Cutter 409" wrote: >>=20 >>> > With Xen-4.1.2: >>> > >>> > I'm trying to change a register value in a paused vmx vcpu. The gener= al >>> > process looks like this: >>> > >>> > 1. Some vmexit calls vcpu_sleep_nosync(v) on the vcpu >>> > 2. From dom0, I issue a domctl to change a register via >>> > v->arch.guest_context.user_reg, then vcpu_wake(v) >>=20 >> Which domctl? From dom0 userspace you can use the libxc functions >> xc_vcpu_getcontext() and xc_vcpu_setcontext() to read/modify register st= ate. >>=20 >> You can read the libxc sources to see what hypercall these map to, if yo= u >> don't want to use libxc for any reason. >>=20 >> =A0-- Keir >>=20 >>> > However, the guest register does not seem to be changed when I do it = this >>> way. >>> > Is there something I need to do to mark the registers as "dirty" ? Is >>> there a >>> > way to force the foreign vcpu to update the changed registers? Or may= be I >>> just >>> > have to change the registers somewhere else? >>> > >>> > I've tried directly using vmcs_enter(v), __vmwrite(), vmcs_exit(v) al= so, >>> but >>> > that doesn't seem to make a change either. >>> > >>> > Thanks! >>> > >>> > >>> > >>> > _______________________________________________ >>> > Xen-devel mailing list >>> > Xen-devel@lists.xen.org >>> > http://lists.xen.org/xen-devel >>=20 >>=20 >=20 >=20 >=20 > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel --B_3428592590_124082462 Content-type: text/html; charset="ISO-8859-1" Content-transfer-encoding: quoted-printable Re: [Xen-devel] Foreign VCPU register change? FWIW I would expect your approach to basically work.

Except... Does your domctl do a vcpu_pause()/vcpu_unpause() on the vcpu? Th= is will ensure that the vcpu is both fully de-scheduled, and all of its regi= ster state is synced back into its vcpu structure.

Otherwise you race the vcpu_sleep_nosync() -- and that’s assuming you= also have a reason for that vcpu to sleep (e.g., non-zero pause counter), e= lse vcpu_sleep_*() operations do nothing!

In short, your problems are almost certainly something to do with the subtl= eties of actually putting a vcpu properly to sleep.

 -- Keir


On 23/08/2012 18:37, "Cutter 409" <cutter409@gmail.com> wrote:

<= SPAN STYLE=3D'font-size:11pt'>I'm making the register change directly from the= hypervisor, inside of the domctl code.

It's a custom domctl that I've added. I'll look into what setcontext does a= fter it modifies the register values, though.

Thank you!

On Thu, Aug 23, 2012 at 1:34 PM, Keir Fraser <keir.xen@gmail.com> wrote:
<= SPAN STYLE=3D'font-size:11pt'>On 23/08/2012 18:25, "Cutter 409" <= cutter409@gmail.com> wrote:

> With Xen-4.1.2:
>
> I'm trying to change a register value in a paused vmx vcpu. The genera= l
> process looks like this:
>
> 1. Some vmexit calls vcpu_sleep_nosync(v) on the vcpu
> 2. From dom0, I issue a domctl to change a register via
> v->arch.guest_context.user_reg, then vcpu_wake(v)

Which domctl? From dom0 userspace you can use the libxc functions
xc_vcpu_getcontext() and xc_vcpu_setcontext() to read/modify register state= .

You can read the libxc sources to see what hypercall these map to, if you don't want to use libxc for any reason.

=A0-- Keir

> However, the guest register does not seem to be changed when I do it t= his way.
> Is there something I need to do to mark the registers as "dirty&q= uot; ? Is there a
> way to force the foreign vcpu to update the changed registers? Or mayb= e I just
> have to change the registers somewhere else?
>
> I've tried directly using vmcs_enter(v), __vmwrite(), vmcs_exit(v) als= o, but
> that doesn't seem to make a change either.
>
> Thanks!
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-deve= l


=

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