RE: [PATCH 07/10] xen/arm: intruduce alloc_domstatic_pages

[Penny Zheng <Penny.Zheng@xxxxxxx>]

Hi Jan

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Friday, May 21, 2021 3:09 PM
> To: Penny Zheng <Penny.Zheng@xxxxxxx>
> Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>; Wei Chen
> <Wei.Chen@xxxxxxx>; nd <nd@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> sstabellini@xxxxxxxxxx; julien@xxxxxxx
> Subject: Re: [PATCH 07/10] xen/arm: intruduce alloc_domstatic_pages
> 
> On 21.05.2021 08:41, Penny Zheng wrote:
> > Hi Jan
> >
> >> -----Original Message-----
> >> From: Jan Beulich <jbeulich@xxxxxxxx>
> >> Sent: Tuesday, May 18, 2021 7:23 PM
> >> To: Penny Zheng <Penny.Zheng@xxxxxxx>
> >> Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>; Wei Chen
> >> <Wei.Chen@xxxxxxx>; nd <nd@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> >> sstabellini@xxxxxxxxxx; julien@xxxxxxx
> >> Subject: Re: [PATCH 07/10] xen/arm: intruduce alloc_domstatic_pages
> >>
> >> On 18.05.2021 10:57, Penny Zheng wrote:
> >>>> From: Jan Beulich <jbeulich@xxxxxxxx>
> >>>> Sent: Tuesday, May 18, 2021 3:35 PM
> >>>>
> >>>> On 18.05.2021 07:21, Penny Zheng wrote:
> >>>>> --- a/xen/common/page_alloc.c
> >>>>> +++ b/xen/common/page_alloc.c
> >>>>> @@ -2447,6 +2447,9 @@ int assign_pages(
> >>>>>      {
> >>>>>          ASSERT(page_get_owner(&pg[i]) == NULL);
> >>>>>          page_set_owner(&pg[i], d);
> >>>>> +        /* use page_set_reserved_owner to set its reserved domain 
> >>>>> owner.
> >>>> */
> >>>>> +        if ( (pg[i].count_info & PGC_reserved) )
> >>>>> +            page_set_reserved_owner(&pg[i], d);
> >>>>
> >>>> Now this is puzzling: What's the point of setting two owner fields
> >>>> to the same value? I also don't recall you having introduced
> >>>> page_set_reserved_owner() for x86, so how is this going to build there?
> >>>>
> >>>
> >>> Thanks for pointing out that it will fail on x86.
> >>> As for the same value, sure, I shall change it to domid_t domid to
> >>> record its
> >> reserved owner.
> >>> Only domid is enough for differentiate.
> >>> And even when domain get rebooted, struct domain may be destroyed,
> >>> but domid will stays The same.
> >>
> >> Will it? Are you intending to put in place restrictions that make it
> >> impossible for the ID to get re-used by another domain?
> >>
> >>> Major user cases for domain on static allocation are referring to
> >>> the whole system are static, No runtime creation.
> >>
> >> Right, but that's not currently enforced afaics. If you would enforce
> >> it, it may simplify a number of things.
> >>
> >>>>> @@ -2509,6 +2512,56 @@ struct page_info *alloc_domheap_pages(
> >>>>>      return pg;
> >>>>>  }
> >>>>>
> >>>>> +/*
> >>>>> + * Allocate nr_pfns contiguous pages, starting at #start, of
> >>>>> +static memory,
> >>>>> + * then assign them to one specific domain #d.
> >>>>> + * It is the equivalent of alloc_domheap_pages for static memory.
> >>>>> + */
> >>>>> +struct page_info *alloc_domstatic_pages(
> >>>>> +        struct domain *d, unsigned long nr_pfns, paddr_t start,
> >>>>> +        unsigned int memflags)
> >>>>> +{
> >>>>> +    struct page_info *pg = NULL;
> >>>>> +    unsigned long dma_size;
> >>>>> +
> >>>>> +    ASSERT(!in_irq());
> >>>>> +
> >>>>> +    if ( memflags & MEMF_no_owner )
> >>>>> +        memflags |= MEMF_no_refcount;
> >>>>> +
> >>>>> +    if ( !dma_bitsize )
> >>>>> +        memflags &= ~MEMF_no_dma;
> >>>>> +    else
> >>>>> +    {
> >>>>> +        dma_size = 1ul << bits_to_zone(dma_bitsize);
> >>>>> +        /* Starting address shall meet the DMA limitation. */
> >>>>> +        if ( dma_size && start < dma_size )
> >>>>> +            return NULL;
> >>>>
> >>>> It is the entire range (i.e. in particular the last byte) which
> >>>> needs to meet such a restriction. I'm not convinced though that DMA
> >>>> width restrictions and static allocation are sensible to coexist.
> >>>>
> >>>
> >>> FWIT, if starting address meets the limitation, the last byte,
> >>> greater than starting address shall meet it too.
> >>
> >> I'm afraid I don't know what you're meaning to tell me here.
> >>
> >
> > Referring to alloc_domheap_pages, if `dma_bitsize` is none-zero value,
> > it will use  alloc_heap_pages to allocate pages from [dma_zone + 1,
> > zone_hi], `dma_zone + 1` pointing to address larger than 2^(dma_zone + 1).
> > So I was setting address limitation for the starting address.
> 
> But does this zone concept apply to static pages at all?
> 

Oh, so sorry. I finally got what you were asking here. Hmm, I was using the 
logic in
bits_to_zone to do the address bits translation. But I got, it will bring 
confusion. I'll
fix it. Thx.

> Jan