Re: [Xen-devel] [PATCH 2/8] x86/setup: Fix badpage= handling for memory above HYPERVISOR_VIRT_END

[Jan Beulich <jbeulich@xxxxxxxx>]

On 01.02.2020 01:32, David Woodhouse wrote:
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -1758,6 +1758,18 @@ int query_page_offline(mfn_t mfn, uint32_t *status)
>      return 0;
>  }
>  
> +static unsigned long contig_avail_pages(struct page_info *pg, unsigned long 
> max_pages)
> +{
> +    unsigned long i;
> +
> +    for ( i = 0 ; i < max_pages; i++)

Nit: Stray blank before first semicolon.

> +    {
> +        if ( pg[i].count_info & PGC_broken )
> +            break;
> +    }
> +    return i;

Further nits: Commonly we omit the braces in cases like this one.
We also like to have blank lines before the main return statement
of a function.

> @@ -1846,6 +1863,63 @@ static unsigned long avail_heap_pages(
>      return free_pages;
>  }
>  
> +static void mark_bad_pages(void)

__init please

> +{
> +    unsigned long bad_spfn, bad_epfn;
> +    const char *p;
> +    struct page_info *pg;
> +#ifdef CONFIG_X86
> +    const struct platform_bad_page *badpage;
> +    unsigned int i, j, array_size;
> +
> +    badpage = get_platform_badpages(&array_size);
> +    if ( badpage )
> +    {
> +        for ( i = 0; i < array_size; i++ )
> +        {
> +            for ( j = 0; j < 1UL << badpage->order; j++ )

Either you mean badpage[i].* here and below, or you're missing an
increment of badpage somewhere.

> +            {
> +                if ( mfn_valid(_mfn(badpage->mfn + j)) )
> +                {
> +                    pg = mfn_to_page(_mfn(badpage->mfn + j));
> +                    pg->count_info |= PGC_broken;
> +                    page_list_add_tail(pg, &page_broken_list);
> +                }
> +            }
> +        }
> +    }
> +#endif
> +
> +    /* Check new pages against the bad-page list. */
> +    p = opt_badpage;
> +    while ( *p != '\0' )
> +    {
> +        bad_spfn = simple_strtoul(p, &p, 0);
> +        bad_epfn = bad_spfn;
> +
> +        if ( *p == '-' )
> +        {
> +            p++;
> +            bad_epfn = simple_strtoul(p, &p, 0);
> +            if ( bad_epfn < bad_spfn )
> +                bad_epfn = bad_spfn;
> +        }
> +
> +        if ( *p == ',' )
> +            p++;
> +        else if ( *p != '\0' )
> +            break;

I think this common (with init_boot_pages()) part of parsing
would better abstracted out, such there will be just one
instance of, and hence there's no risk of things going out of
sync.

> +        while ( mfn_valid(_mfn(bad_spfn)) && bad_spfn < bad_epfn )

As per init_boot_pages() as well as per the "bad_epfn = bad_spfn;"
you have further up, the range here is inclusive at its end. I'm
also uncertain about the stopping at the first !mfn_valid() -
there may well be further valid pages later on.

Jan

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