[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH RFC] pvh: clearly specify used parameters in vcpu_guest_context

On 15/11/13 23:56, Mukesh Rathor wrote:
On Fri, 15 Nov 2013 13:56:54 -0800
Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:

On Fri, 15 Nov 2013 16:45:47 +0000
"Jan Beulich" <JBeulich@xxxxxxxx> wrote:

On 15.11.13 at 17:40, George Dunlap
<george.dunlap@xxxxxxxxxxxxx> wrote:
On 15/11/13 16:32, Jan Beulich wrote:
On 15.11.13 at 16:50, Roger Pau Monne <roger.pau@xxxxxxxxxx>
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -704,9 +704,11 @@ int arch_set_info_guest(
           /* PVH 32bitfixme */
- if ( c(ctrlreg[1]) || c(ldt_base) || c(ldt_ents) ||
+        if ( c(ctrlreg[0]) || c(ctrlreg[1]) || c(ctrlreg[2]) ||
+             c(ctrlreg[4]) || c(ldt_base) || c(ldt_ents) ||
I think it should actually be a bug for the guest to request an
all blank CR0 or CR4. Minimally CR0.PE, CR0.PG, and CR4.PAE
would seem to be a valid requirement to be set.

Apart from that ctrlreg[] is an 8-element array... And I don't
see debugreg[] being verified at all.

                c(user_regs.cs) || c(user_regs.ss) ||
c(user_regs.es) || c(user_regs.ds) || c(user_regs.fs) ||
c(user_regs.gs) ||
+             c(kernel_ss) || c(kernel_sp) ||
c.nat->gs_base_kernel ||
So George and/or Mukesh found it necessary to set
gs_base_kernel, and you rip it out? I'm curious as to what
they're going to say...
I didn't find it necessary; I was mostly focused on merging the
PVH and HVM codepaths without causing any regressions.  It's not
obvious to me what's special about gs_base_kernel, and I haven't
yet gone back to try to find out why Mukesh did it that way.

We had talked about this while ago, but upon boot, the first thing
a vcpu needs is access to kernel data structure. (A secondary vcpu
is bootstrapped way up into the kernel). It would be possible to
get rid of gs_base_kernel, but will take some work on the linux side.
I can try and test it out, and let you guys know.
Ok, looking at this more, I can hack cpu_bringup_and_idle() in
linux to include a static variable for cpuid, which is the least a
vcpu needs to know first thing. But, I think that would not work when
vcpu hotplug support is added. Another option would be to pass cpuid
in one of the registers, say rdi. Thus, rdi == cpuid will be passed
to VCPUOP_initialise. In bringup function, the booting vcpu can then
load it's own gs based on the cpuid. If linux folks, konrad (CCd), is OK
with this, we can remove gs_base_kernel.  Otherwise, it's such a small
thing, hopefually it can stay.

So Linux has the exact same problem on native, and (AFAICT) they solve it by simply writing gs to a global variable called initial_gs. Is there any reason why we can't just do what native Linux does here? We should, in fact, be able to use the exact same variable.


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.