Re: [PATCH 07/22] x86/pv: domheap pages should be mapped while relocating initrd

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.12.2022 12:48, Julien Grall wrote:
> From: Wei Liu <wei.liu2@xxxxxxxxxx>
> 
> Xen shouldn't use domheap page as if they were xenheap pages. Map and
> unmap pages accordingly.
> 
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> Signed-off-by: Wei Wang <wawei@xxxxxxxxx>
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> 
> ----
> 
>     Changes since Hongyan's version:
>         * Add missing newline after the variable declaration
> ---
>  xen/arch/x86/pv/dom0_build.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/x86/pv/dom0_build.c b/xen/arch/x86/pv/dom0_build.c
> index a62f0fa2ef29..c837b2d96f89 100644
> --- a/xen/arch/x86/pv/dom0_build.c
> +++ b/xen/arch/x86/pv/dom0_build.c
> @@ -611,18 +611,32 @@ int __init dom0_construct_pv(struct domain *d,
>          if ( d->arch.physaddr_bitsize &&
>               ((mfn + count - 1) >> (d->arch.physaddr_bitsize - PAGE_SHIFT)) )
>          {
> +            unsigned long nr_pages;
> +            unsigned long len = initrd_len;
> +
>              order = get_order_from_pages(count);
>              page = alloc_domheap_pages(d, order, MEMF_no_scrub);
>              if ( !page )
>                  panic("Not enough RAM for domain 0 initrd\n");
> +
> +            nr_pages = 1UL << order;

I don't think this needs establishing here and ...

>              for ( count = -count; order--; )
>                  if ( count & (1UL << order) )
>                  {
>                      free_domheap_pages(page, order);
>                      page += 1UL << order;
> +                    nr_pages -= 1UL << order;

... updating here. Doing so just once ...

>                  }
> -            memcpy(page_to_virt(page), mfn_to_virt(initrd->mod_start),
> -                   initrd_len);
> +

... here ought to suffice, assuming this 2nd variable is needed at all
(alongside "len").

> +            for ( i = 0; i < nr_pages; i++, len -= PAGE_SIZE )
> +            {
> +                void *p = __map_domain_page(page + i);
> +
> +                memcpy(p, mfn_to_virt(initrd_mfn + i),
> +                       min(len, (unsigned long)PAGE_SIZE));
> +                unmap_domain_page(p);
> +            }

You're half open-coding copy_domain_page() without saying anywhere why
the remaining mfn_to_virt() is okay to keep. If you used
copy_domain_page(), no such remark would need adding in the description.

Jan