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RE: [PATCH v11 6/6] xen: retrieve reserved pages on populate_physmap
- To: Julien Grall <julien@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Penny Zheng <Penny.Zheng@xxxxxxx>
- Date: Fri, 2 Sep 2022 07:10:34 +0000
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- Cc: Wei Chen <Wei.Chen@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Fri, 02 Sep 2022 07:10:50 +0000
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- Thread-topic: [PATCH v11 6/6] xen: retrieve reserved pages on populate_physmap
Hi Julien
> -----Original Message-----
> From: Julien Grall <julien@xxxxxxx>
> Sent: Thursday, September 1, 2022 9:53 PM
> To: Penny Zheng <Penny.Zheng@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Wei Chen <Wei.Chen@xxxxxxx>; Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>; George Dunlap <george.dunlap@xxxxxxxxxx>;
> Jan Beulich <jbeulich@xxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>;
> Wei Liu <wl@xxxxxxx>
> Subject: Re: [PATCH v11 6/6] xen: retrieve reserved pages on
> populate_physmap
>
> Hi Penny,
>
> On 31/08/2022 03:40, Penny Zheng wrote:
> > +/*
> > + * Acquire a page from reserved page list(resv_page_list), when
> > +populating
> > + * memory for static domain on runtime.
> > + */
> > +mfn_t acquire_reserved_page(struct domain *d, unsigned int memflags)
> > +{
> > + struct page_info *page;
> > +
> > + ASSERT_ALLOC_CONTEXT();
> > +
> > + /* Acquire a page from reserved page list(resv_page_list). */
> > + spin_lock(&d->page_alloc_lock);
> > + page = page_list_remove_head(&d->resv_page_list);
> > + spin_unlock(&d->page_alloc_lock);
> > + if ( unlikely(!page) )
> > + return INVALID_MFN;
> > +
> > + if ( !prepare_staticmem_pages(page, 1, memflags) )
> > + goto fail;
> > +
> > + if ( assign_domstatic_pages(d, page, 1, memflags) )
> > + goto fail_assign;
> > +
> > + return page_to_mfn(page);
> > +
> > + fail_assign:
> > + unprepare_staticmem_pages(page, 1, false);
>
> Looking at assign_domstatic_pages(). It will already call
> unprepare_staticmem_pages() in one of the error path. It doesn't look like
> the latter can be called twice on a page.
>
> To be honest, I find a bit odd that assign_domstatic_pages() is calling
> unprepare_staticmem_pages() because the former doesn't call the "prepare"
> function.
>
> AFAICT, this is an issue introduced in this patch. So I would remove the call
> from assign_domstatic_pages() and then let the caller calls
> unprepare_staticmem_pages() (this would need to be added in
> acquire_domstatic_pages()).
>
True, true, thanks for pointing out!!
> Also, I think it would be good to explain why we don't need to scrub.
> Something like:
>
> "The page was never accessible by the domain. So scrubbing can be skipped".
>
Ok, I'll add in-code comment
> Cheers,
>
> --
> Julien Grall
|
