RE: [PATCH 04/10] xen/arm: static memory initialization

[Penny Zheng <Penny.Zheng@xxxxxxx>]

Hi Julien

> -----Original Message-----
> From: Julien Grall <julien@xxxxxxx>
> Sent: Tuesday, May 18, 2021 6:01 PM
> To: Penny Zheng <Penny.Zheng@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> sstabellini@xxxxxxxxxx
> Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>; Wei Chen
> <Wei.Chen@xxxxxxx>; nd <nd@xxxxxxx>
> Subject: Re: [PATCH 04/10] xen/arm: static memory initialization
> 
> Hi Penny,
> 
> On 18/05/2021 06:21, Penny Zheng wrote:
> > This patch introduces static memory initialization, during system RAM boot
> up.
> >
> > New func init_staticmem_pages is the equivalent of init_heap_pages,
> > responsible for static memory initialization.
> >
> > Helper func free_staticmem_pages is the equivalent of free_heap_pages,
> > to free nr_pfns pages of static memory.
> > For each page, it includes the following steps:
> > 1. change page state from in-use(also initialization state) to free
> > state and grant PGC_reserved.
> > 2. set its owner NULL and make sure this page is not a guest frame any
> > more 3. follow the same cache coherency policy in free_heap_pages 4.
> > scrub the page in need
> >
> > Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> > ---
> >   xen/arch/arm/setup.c    |  2 ++
> >   xen/common/page_alloc.c | 70
> +++++++++++++++++++++++++++++++++++++++++
> >   xen/include/xen/mm.h    |  3 ++
> >   3 files changed, 75 insertions(+)
> >
> > diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c index
> > 444dbbd676..f80162c478 100644
> > --- a/xen/arch/arm/setup.c
> > +++ b/xen/arch/arm/setup.c
> > @@ -818,6 +818,8 @@ static void __init setup_mm(void)
> >
> >       setup_frametable_mappings(ram_start, ram_end);
> >       max_page = PFN_DOWN(ram_end);
> > +
> > +    init_staticmem_pages();
> >   }
> >   #endif
> >
> > diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c index
> > ace6333c18..58b53c6ac2 100644
> > --- a/xen/common/page_alloc.c
> > +++ b/xen/common/page_alloc.c
> > @@ -150,6 +150,9 @@
> >   #define p2m_pod_offline_or_broken_hit(pg) 0
> >   #define p2m_pod_offline_or_broken_replace(pg) BUG_ON(pg != NULL)
> >   #endif
> > +#ifdef CONFIG_ARM_64
> > +#include <asm/setup.h>
> > +#endif
> >
> >   /*
> >    * Comma-separated list of hexadecimal page numbers containing bad
> bytes.
> > @@ -1512,6 +1515,49 @@ static void free_heap_pages(
> >       spin_unlock(&heap_lock);
> >   }
> >
> > +/* Equivalent of free_heap_pages to free nr_pfns pages of static
> > +memory. */ static void free_staticmem_pages(struct page_info *pg,
> > +unsigned long nr_pfns,
> 
> This function is dealing with MFNs, so the second parameter should be called
> nr_mfns.
> 

Agreed, thx.

> > +                                 bool need_scrub) {
> > +    mfn_t mfn = page_to_mfn(pg);
> > +    int i;
> > +
> > +    for ( i = 0; i < nr_pfns; i++ )
> > +    {
> > +        switch ( pg[i].count_info & PGC_state )
> > +        {
> > +        case PGC_state_inuse:
> > +            BUG_ON(pg[i].count_info & PGC_broken);
> > +            /* Make it free and reserved. */
> > +            pg[i].count_info = PGC_state_free | PGC_reserved;
> > +            break;
> > +
> > +        default:
> > +            printk(XENLOG_ERR
> > +                   "Page state shall be only in PGC_state_inuse. "
> > +                   "pg[%u] MFN %"PRI_mfn" count_info=%#lx
> tlbflush_timestamp=%#x.\n",
> > +                   i, mfn_x(mfn) + i,
> > +                   pg[i].count_info,
> > +                   pg[i].tlbflush_timestamp);
> > +            BUG();
> > +        }
> > +
> > +        /*
> > +         * Follow the same cache coherence scheme in free_heap_pages.
> > +         * If a page has no owner it will need no safety TLB flush.
> > +         */
> > +        pg[i].u.free.need_tlbflush = (page_get_owner(&pg[i]) != NULL);
> > +        if ( pg[i].u.free.need_tlbflush )
> > +            page_set_tlbflush_timestamp(&pg[i]);
> > +
> > +        /* This page is not a guest frame any more. */
> > +        page_set_owner(&pg[i], NULL);
> > +        set_gpfn_from_mfn(mfn_x(mfn) + i, INVALID_M2P_ENTRY);
> 
> The code looks quite similar to free_heap_pages(). Could we possibly create
> an helper which can be called from both?
> 

Ok, I will extract the common code here and there.
 
> > +
> > +        if ( need_scrub )
> > +            scrub_one_page(&pg[i]);
> 
> So the scrubbing will be synchronous. Is it what we want?
> 
> You also seem to miss the flush the call to flush_page_to_ram().
> 

Yeah, right now, it is synchronous.
I guess that it is not an optimal choice, only a workable one right now.
I'm trying to borrow some asynchronous scrubbing ideas from heap in the future.

Yes! If we are doing synchronous scrubbing, we need to flush_page_to_ram(). Thx.

> > +    }
> > +}
> >
> >   /*
> >    * Following rules applied for page offline:
> > @@ -1828,6 +1874,30 @@ static void init_heap_pages(
> >       }
> >   }
> >
> > +/* Equivalent of init_heap_pages to do static memory initialization
> > +*/ void __init init_staticmem_pages(void) {
> > +    int bank;
> > +
> > +    /*
> > +     * TODO: Considering NUMA-support scenario.
> > +     */
> > +    for ( bank = 0 ; bank < bootinfo.static_mem.nr_banks; bank++ )
> 
> bootinfo is arm specific, so this code should live in arch/arm rather than
> common/.
> 

Yes, I'm considering to create a new CONFIG_STATIC_MEM to include all
static-memory-related functions.

> > +    {
> > +        paddr_t bank_start = bootinfo.static_mem.bank[bank].start;
> > +        paddr_t bank_size = bootinfo.static_mem.bank[bank].size;
> > +        paddr_t bank_end = bank_start + bank_size;
> > +
> > +        bank_start = round_pgup(bank_start);
> > +        bank_end = round_pgdown(bank_end);
> > +        if ( bank_end <= bank_start )
> > +            return;
> > +
> > +        free_staticmem_pages(maddr_to_page(bank_start),
> > +                            (bank_end - bank_start) >> PAGE_SHIFT, false);
> > +    }
> > +}
> > +
> >   static unsigned long avail_heap_pages(
> >       unsigned int zone_lo, unsigned int zone_hi, unsigned int node)
> >   {
> > diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h index
> > 667f9dac83..8b1a2207b2 100644
> > --- a/xen/include/xen/mm.h
> > +++ b/xen/include/xen/mm.h
> > @@ -85,6 +85,9 @@ bool scrub_free_pages(void);
> >   } while ( false )
> >   #define FREE_XENHEAP_PAGE(p) FREE_XENHEAP_PAGES(p, 0)
> >
> > +/* Static Memory */
> > +void init_staticmem_pages(void);
> > +
> >   /* Map machine page range in Xen virtual address space. */
> >   int map_pages_to_xen(
> >       unsigned long virt,
> >
> 
> Cheers,
> 
> --
> Julien Grall

Cheers

Penny