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Re: [PATCH] docs: fix INTRODUCE description in xenstore.txt
- To: Juergen Gross <jgross@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 5 Mar 2025 22:57:44 +0000
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- Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
- Delivery-date: Wed, 05 Mar 2025 22:58:02 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 05/03/2025 8:52 am, Juergen Gross wrote:
> The description of the Xenstore INTRODUCE command is still referencing
> xend. Fix that.
>
> While at it, make clear that the Xenstore implementation is allowed
> to ignore the specified gfn and use the Xenstore reserved grant id
> GNTTAB_RESERVED_XENSTORE instead.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> docs/misc/xenstore.txt | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/docs/misc/xenstore.txt b/docs/misc/xenstore.txt
> index 38015835b1..d894d24d11 100644
> --- a/docs/misc/xenstore.txt
> +++ b/docs/misc/xenstore.txt
> @@ -286,7 +286,7 @@ TRANSACTION_END F|
> INTRODUCE <domid>|<gfn>|<evtchn>|?
> Notifies xenstored to communicate with this domain.
>
> - INTRODUCE is currently only used by xend (during domain
> + INTRODUCE is currently only used by xen tools (during domain
> startup and various forms of restore and resume), and
> xenstored prevents its use other than by dom0.
>
> @@ -299,6 +299,10 @@ INTRODUCE <domid>|<gfn>|<evtchn>|?
> for example passing a high-bit-set 32-bit gfn as an unsigned
> decimal will attempt to use 0x7fffffff instead (!).
>
> + Xenstored might ignore the <gfn> value and use the reserved
> + grant table entry GNTTAB_RESERVED_XENSTORE instead for mapping
> + the Xenstore interface page of the guest.
I'd suggest making a stronger statement than this.
---
The <gfn> field is used by xenstoreds which use foreign mapping to
access the ring page.
Alternatively, Grant 1 (GNTTAB_RESERVED_XENSTORE) is reserved for the
same purpose, and is populated by the domain builder on behalf of the
guest. This mechanism is preferred because reduces the permissions that
xenstored needs in order to function.
Both <gfn> and Grant 1 need to agree, because implementations of
xenstored will use one and ignore the other.
---
~Andrew
|
