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Re: [RFC PATCH] xen/gnttab: Store frame GFN in struct page_info on Arm
- To: Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 13 Sep 2021 08:17:38 +0200
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- Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 13 Sep 2021 06:18:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10.09.2021 09:52, Jan Beulich wrote:
> On 10.09.2021 01:04, Oleksandr Tyshchenko wrote:
>> @@ -731,11 +733,19 @@ static void p2m_put_l3_page(const lpae_t pte)
>> */
>> if ( p2m_is_foreign(pte.p2m.type) )
>> {
>> - mfn_t mfn = lpae_get_mfn(pte);
>> -
>> ASSERT(mfn_valid(mfn));
>> put_page(mfn_to_page(mfn));
>> }
>> +
>> +#ifdef CONFIG_GRANT_TABLE
>> + /*
>> + * Check whether we deal with grant table page. As the grant table page
>> + * is xen_heap page and its entry has known p2m type, detect it and mark
>> + * the stored GFN as invalid.
>> + */
>> + if ( p2m_is_ram(pte.p2m.type) && is_xen_heap_mfn(mfn) )
>> + page_set_frame_gfn(mfn_to_page(mfn), INVALID_GFN);
>> +#endif
>
> I take it the write done is benign for other Xen heap pages? I suppose
> this would want making very explicit, as such an assumption is easy to
> go stale by entirely unrelated changes.
>
> I also wonder whether you really mean to include p2m_ram_ro pages here
> as well.
Actually I've meanwhile realized I should put my question here quite
differently: Aren't you effectively introducing an M2P here for Arm,
except that you artificially limit it to the Xen heap pages needed for
the grant table?
Jan
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