RE: [PATCH 4/9] xen/arm: static memory initialization

[Penny Zheng <Penny.Zheng@xxxxxxx>]

Hi Julien

> -----Original Message-----
> From: Julien Grall <julien@xxxxxxx>
> Sent: Thursday, July 1, 2021 2:10 AM
> To: Penny Zheng <Penny.Zheng@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
> sstabellini@xxxxxxxxxx; jbeulich@xxxxxxxx
> Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>; Wei Chen
> <Wei.Chen@xxxxxxx>
> Subject: Re: [PATCH 4/9] xen/arm: static memory initialization
> 
> Hi Penny,
> 
> On 07/06/2021 03:43, Penny Zheng wrote:
> > This patch introduces static memory initialization, during system RAM boot
> up.
> 
> The word "RAM" looks spurious.
> 

Thx. I check the "spurious" in dictionary, it means fake? So I will leave 
"during system boot up"
here.

> > New func init_staticmem_pages is responsible for static memory
> initialization.
> 
> s/New func/The new function/
>
 
Sure. thx

> > Helper free_staticmem_pages is the equivalent of free_heap_pages, to
> > free nr_mfns pages of static memory.
> >
> > This commit defines a new helper free_page to extract common code
> > between free_heap_pages and free_staticmem_pages, like following the
> > same cache/TLB coherency policy.
> >
> > For each page, free_staticmem_pages includes the following extra steps
> > to
> > initialize:
> > 1. change page state from inuse to free state and grant PGC_reserved.
> 
> I think you mean "set" rather than "grant".
> 

Yeah.  I'll change to set here~

> > 2. scrub the page in need synchronously.
> 
> Can you explain why this is necessary?
>

Since I'm borrowing the logic in free_heap_pages, I'm also trying to cover all 
the scenarios here like it does.
So I assume that free_staticmem_page will not only be used on initialization, 
but also when destroying/rebooting the domain.
On these cases, it is necessary to scrub the page, ig.
 
> >
> > Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> > ---
> > changes v2:
> > - rename to nr_mfns
> > - extract common code from free_heap_pages and free_staticmem_pages
> > - remove dead codes in other archs, including move some to
> > arm-specific file, and put some under CONFIG_ARM
> > - mark free_staticmem_pages __init
> > ---
> >   xen/arch/arm/setup.c    | 27 ++++++++++++++
> 
> I think it would be best to split the arm use in a separate patch.

Sure, I'll move them to another commit.

> 
> >   xen/common/page_alloc.c | 78 +++++++++++++++++++++++++++++++++---
> -----
> >   xen/include/xen/mm.h    |  6 ++++
> >   3 files changed, 97 insertions(+), 14 deletions(-)
> >
> > diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c index
> > 00aad1c194..daafea0abb 100644
> > --- a/xen/arch/arm/setup.c
> > +++ b/xen/arch/arm/setup.c
> > @@ -611,6 +611,30 @@ static void __init init_pdx(void)
> >       }
> >   }
> >
> > +/* Static memory initialization */
> > +static void __init init_staticmem_pages(void) {
> > +    int bank;
> > +
> > +    /*
> > +     * TODO: Considering NUMA-support scenario.
> > +     */
> > +    for ( bank = 0 ; bank < bootinfo.static_mem.nr_banks; bank++ )
> > +    {
> > +        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);
> > +    }
> > +}
> > +
> >   #ifdef CONFIG_ARM_32
> >   static void __init setup_mm(void)
> >   {
> > @@ -872,6 +896,9 @@ void __init start_xen(unsigned long
> boot_phys_offset,
> >       cmdline_parse(cmdline);
> >
> >       setup_mm();
> > +    /* If exists, Static Memory Initialization. */
> > +    if ( bootinfo.static_mem.nr_banks > 0 )
> 
> This check seems a pointless because init_staticmem_pages() is already able
> to cope with nr_banks == 0.
> 
> > +        init_staticmem_pages();
> I would prefer if this is folded in setup_mm().
>

Sure.
 
> >
> >       /* Parse the ACPI tables for possible boot-time configuration */
> >       acpi_boot_table_init();
> > diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c index
> > 958ba0cd92..8c00262c04 100644
> > --- a/xen/common/page_alloc.c
> > +++ b/xen/common/page_alloc.c
> > @@ -1376,6 +1376,37 @@ bool scrub_free_pages(void)
> >       return node_to_scrub(false) != NUMA_NO_NODE;
> >   }
> >
> > +static void free_page(struct page_info *pg, bool need_scrub) {
> > +    mfn_t mfn = page_to_mfn(pg);
> > +
> > +    /* If a page has no owner it will need no safety TLB flush. */
> > +    pg->u.free.need_tlbflush = (page_get_owner(pg) != NULL);
> > +    if ( pg->u.free.need_tlbflush )
> > +        page_set_tlbflush_timestamp(pg);
> > +
> > +    /* This page is not a guest frame any more. */
> > +    page_set_owner(pg, NULL); /* set_gpfn_from_mfn snoops pg owner */
> > +    set_gpfn_from_mfn(mfn_x(mfn), INVALID_M2P_ENTRY);
> > +
> > +#ifdef CONFIG_ARM
> 
> To echo what Jan already wrote, I am not in favor of adding new #ifdef
> CONFIG_<arch> in common code. I would expect the logic for static memory
> to be the same for each arch, so this should be protected with a generic
> Kconfig.
> 
> > +    if ( pg->count_info & PGC_reserved )
> > +    {
> > +        /* TODO: asynchronous scrubbing. */
> > +        if ( need_scrub )
> > +            scrub_one_page(pg);
> > +        return;
> > +    }
> > +#endif
> > +    if ( need_scrub )
> > +    {
> > +        pg->count_info |= PGC_need_scrub;
> > +        poison_one_page(pg);
> > +    }
> > +
> > +    return;
> > +}
> > +
> >   /* Free 2^@order set of pages. */
> >   static void free_heap_pages(
> >       struct page_info *pg, unsigned int order, bool need_scrub) @@
> > -1425,20 +1456,7 @@ static void free_heap_pages(
> >               BUG();
> >           }
> >
> > -        /* 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 snoops pg
> owner */
> > -        set_gpfn_from_mfn(mfn_x(mfn) + i, INVALID_M2P_ENTRY);
> > -
> > -        if ( need_scrub )
> > -        {
> > -            pg[i].count_info |= PGC_need_scrub;
> > -            poison_one_page(&pg[i]);
> > -        }
> > +        free_page(&pg[i], need_scrub);
> >       }
> >
> >       avail[node][zone] += 1 << order; @@ -1512,6 +1530,38 @@ static
> > void free_heap_pages(
> >       spin_unlock(&heap_lock);
> >   }
> >
> > +#ifdef CONFIG_STATIC_ALLOCATION
> > +/* Equivalent of free_heap_pages to free nr_mfns pages of static
> > +memory. */ void __init free_staticmem_pages(struct page_info *pg,
> unsigned long nr_mfns,
> > +                                 bool need_scrub) {
> > +    mfn_t mfn = page_to_mfn(pg);
> > +    unsigned long i;
> > +
> > +    for ( i = 0; i < nr_mfns; i++ )
> > +    {
> > +        switch ( pg[i].count_info & PGC_state )
> > +        {
> > +        case PGC_state_inuse:
> > +            BUG_ON(pg[i].count_info & PGC_broken);
> > +            /* Mark 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[%lu] MFN %"PRI_mfn" count_info=%#lx
> tlbflush_timestamp=%#x.\n",
> > +                   i, mfn_x(mfn) + i,
> > +                   pg[i].count_info,
> > +                   pg[i].tlbflush_timestamp);
> > +            BUG();
> > +        }
> > +
> > +        free_page(&pg[i], need_scrub);
> > +    }
> > +}
> > +#endif
> >
> >   /*
> >    * Following rules applied for page offline:
> > diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h index
> > 667f9dac83..df25e55966 100644
> > --- a/xen/include/xen/mm.h
> > +++ b/xen/include/xen/mm.h
> > @@ -85,6 +85,12 @@ bool scrub_free_pages(void);
> >   } while ( false )
> >   #define FREE_XENHEAP_PAGE(p) FREE_XENHEAP_PAGES(p, 0)
> >
> > +#ifdef CONFIG_ARM
> > +/* Static Allocation */
> > +void free_staticmem_pages(struct page_info *pg, unsigned long nr_mfns,
> > +                          bool need_scrub); #endif
> > +
> >   /* Map machine page range in Xen virtual address space. */
> >   int map_pages_to_xen(
> >       unsigned long virt,
> >
> 
> --
> Julien Grall


Cheers
Penny Zheng