Re: [Xen-devel] [PATCH for-4.12 1/8] dom0/pvh: align allocation and mapping order to start address

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Jan 30, 2019 at 11:36:39AM +0100, Roger Pau Monne wrote:
> Due to the recent changes in the iommu mapping logic, the start
> addresses provided need to be aligned to the order intended to be
> mapped.
> 

Can you reference some commits here? What would happen if the address is
not aligned?

> dom0 PVH domain builder didn't take this into account when populating
> the p2m, fix this by making sure the order is chosen so that the start
> address is aligned to it.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
> Without this patch trying to create a PVH dom0 will trigger an assert
> on certain hardware depending on the memory map.
> ---
>  xen/arch/x86/hvm/dom0_build.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/xen/arch/x86/hvm/dom0_build.c b/xen/arch/x86/hvm/dom0_build.c
> index 51cf490811..a571d15c13 100644
> --- a/xen/arch/x86/hvm/dom0_build.c
> +++ b/xen/arch/x86/hvm/dom0_build.c
> @@ -152,6 +152,8 @@ static int __init pvh_populate_memory_range(struct domain 
> *d,
>  
>          order = get_order_from_pages(end - start + 1);
>          order = min(order ? order - 1 : 0, max_order);
> +        /* The order allocated and populated must be aligned to the address. 
> */
> +        order = min(order, start ? find_first_set_bit(start) : MAX_ORDER);

Isn't max_order better here?

>          page = alloc_domheap_pages(d, order, dom0_memflags | MEMF_no_scrub);
>          if ( page == NULL )
>          {
> -- 
> 2.20.1
> 

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