Re: [PATCH v5 9/9] xen: retrieve reserved pages on populate_physmap

[Jan Beulich <jbeulich@xxxxxxxx>]

On 31.05.2022 05:12, Penny Zheng wrote:
> --- a/xen/common/memory.c
> +++ b/xen/common/memory.c
> @@ -245,6 +245,29 @@ static void populate_physmap(struct memop_args *a)
>  
>                  mfn = _mfn(gpfn);
>              }
> +            else if ( is_domain_using_staticmem(d) )
> +            {
> +                /*
> +                 * No easy way to guarantee the retrieved pages are 
> contiguous,
> +                 * so forbid non-zero-order requests here.
> +                 */
> +                if ( a->extent_order != 0 )
> +                {
> +                    gdprintk(XENLOG_WARNING,
> +                             "Cannot allocate static order-%u pages for 
> static %pd\n",
> +                             a->extent_order, d);
> +                    goto out;
> +                }
> +
> +                mfn = acquire_reserved_page(d, a->memflags);
> +                if ( mfn_eq(mfn, INVALID_MFN) )
> +                {
> +                    gdprintk(XENLOG_WARNING,
> +                             "%pd: failed to retrieve a reserved page\n",
> +                             d);
> +                    goto out;
> +                }
> +            }

I'm not convinced of having these gdprintk()s here. The adjacent
is_domain_direct_mapped() code is somewhat different - iirc only Dom0
can be direct-mapped, and Dom0 having a problem can certainly be worth
a log message.

> +/*
> + * Acquire a page from reserved page list(resv_page_list), when populating
> + * memory for static domain on runtime.
> + */
> +mfn_t acquire_reserved_page(struct domain *d, unsigned int memflags)
> +{
> +    struct page_info *page;
> +
> +    spin_lock(&d->page_alloc_lock);
> +    /* Acquire a page from reserved page list(resv_page_list). */
> +    page = page_list_remove_head(&d->resv_page_list);
> +    if ( unlikely(!page) )
> +        return INVALID_MFN;
> +    spin_unlock(&d->page_alloc_lock);

You want to drop the lock before returning.

Jan