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: 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.   

> Jan

Cheers

Penny