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Re: [PATCH] x86/pv: Drop stale comment in dom0_construct_pv()

  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Thu, 29 Oct 2020 19:14:48 +0000
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  • Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Thu, 29 Oct 2020 19:15:01 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 29/10/2020 14:37, Jan Beulich wrote:
> On 29.10.2020 15:00, Andrew Cooper wrote:
>> This comment has been around since c/s 1372bca0615 in 2004.  It is stale, as
>> it predates the introduction of struct vcpu.
> That commit only moved it around; it's 22a857bde9b8 afaics from
> early 2003 where it first appeared, where it had a reason:
>     /*
>      * WARNING: The new domain must have its 'processor' field
>      * filled in by now !!
>      */
>     phys_l2tab = ALLOC_FRAME_FROM_DOMAIN();
>     l2tab = map_domain_mem(phys_l2tab);
>     memcpy(l2tab, idle_pg_table[p->processor], PAGE_SIZE);

Oh yes - my simple search didn't spot the reformat.

> But yes, the comment has been stale for a long time, and I've
> been wondering a number of times what it was supposed to tell
> me. (I think it was already stale at the point the comment
> first got altered, in 3072fef54df8.)

Looks like it became stale with 99db02d5097 "Remove CPU-dependent
page-directory entries." which drops the per-cpu idle_pg_table.

>> It is not obvious that it was even correct at the time.  Where a vcpu (domain
>> at the time) has been configured to run is unrelated to construct the 
>> domain's
>> initial pagetables, etc.
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Thanks.  I'll update the commit message.




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