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Re: [PATCH v3 07/18] x86/hvm: introduce per-vCPU L3 page-table
- To: George Dunlap <gwd@xxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 9 Oct 2026 09:06:55 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger@xxxxxxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 09 Oct 2026 07:07:18 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08.10.2026 23:00, George Dunlap wrote:
> On Thu, Oct 8, 2026 at 9:40 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 07.10.2026 12:40, George Dunlap wrote:
>>> --- a/xen/arch/x86/pv/domain.c
>>> +++ b/xen/arch/x86/pv/domain.c
>>> @@ -127,7 +127,7 @@ static int setup_compat_l4(struct vcpu *v)
>>> mfn = page_to_mfn(pg);
>>> l4tab = map_domain_page(mfn);
>>> clear_page(l4tab);
>>> - init_xen_l4_slots(l4tab, mfn, v->domain, INVALID_MFN, false);
>>> + init_xen_l4_slots(l4tab, mfn, v->domain, v, INVALID_MFN, false);
>>
>> This being PV-only code, don't you want to pass NULL here? The description
>> talks about this, but (a) it's not quite clear why PV32 would want handling
>> differently from PV64 at this point and (b) in sh_make_shadow() you do pass
>> NULL unconditionally.
>
> This is actually left over from the previous iteration of the series
> which supports PV guests; and apparently it would be a lot easier for
> implement per-vCPU pagetables for 32-bit PV guests, since the L4
> doesn't belong to the guest. But it's outside of the scope of the
> current work.
>
> At any rate, I'm going to try passing a single vcpu, as Roger
> suggested. That restricts toolstacks to not being able to promote PV
> L4s before calling XEN_DOMCTL_max_vcpus, but that seems fine to me.
But my question was why it's not NULL that is being passed here.
Jan
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