On 23/12/2019 18:23, Julien Grall wrote:
> Hi,
>
> On 17/12/2019 21:15, Andrew Cooper wrote:
>> xc_dom_p2m() and dom->p2m_host[] implement a linear transform for
>> translated
>> domains, but waste a substantial chunk of RAM doing so.
>>
>> ARM literally never reads dom->p2m_host[] (because of the
>> xc_dom_translated()
>> short circuit in xc_dom_p2m()). Drop it all.
>>
>> x86 HVM does use dom->p2m_host[] for
>> xc_domain_populate_physmap_exact() calls
>> when populating 4k pages. Reuse the same tactic from 2M/1G ranges
>> and use an
>> on-stack array instead. Drop the memory allocation.
>>
>> x86 PV guests do use dom->p2m_host[] as a non-identity transform.
>> Rename the
>> field to pv_p2m to make it clear it is PV-only.
>
> Nice cleanup! This will probably make slightly faster guest boot :).
>
>> @@ -359,7 +356,6 @@ static int populate_guest_memory(struct
>> xc_dom_image *dom,
>> static int meminit(struct xc_dom_image *dom)
>> {
>> int i, rc;
>> - xen_pfn_t pfn;
>> uint64_t modbase;
>> uint64_t ramsize = (uint64_t)dom->total_pages << XC_PAGE_SHIFT;
>> @@ -423,11 +419,6 @@ static int meminit(struct xc_dom_image *dom)
>> assert(ramsize == 0); /* Too much RAM is rejected above */
>> dom->p2m_size = p2m_size;
>
> Do we need to keep p2m_size?
Yes, I think so.
There are some common checks which would fail if it becomes 0, and
importantly, it is used to locate safe gfns for temporary physmap mappings.
~Andrew
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