Re: [XEN RFC PATCH 05/40] xen/arm: Fix lowmem_bitsize when arch_get_dma_bitsize return 0

[Julien Grall <julien@xxxxxxx>]

Hi,

I guess this patch may be dropped after my comment on patch #4. I will 
comment just on the process.
On 11/08/2021 11:23, Wei Chen wrote:
> From: Hongda Deng <Hongda.Deng@xxxxxxx>
>
> In previous patch, we make arch_get_dma_bitsize return 0 when
> dma_bitsize and platform->dma_bitsize are not set. But this
> will affect lowmem_bitsize in allocate_memory_11 for domain0.
> Because this function depends lowmem_bitsize to allocate memory
> below 4GB.
>
> In current code, when arch_get_dma_bitsize return 0, lowmem_bitsize
> will be set to 0. In this case, we will get "No bank has been
> allocated below 0-bit." message while allocating domain0 memory.
> And the lowmem will be set to false.
>
> This behavior is inconsistent with what allocate_memory_11 done
> before, and doesn't meet this functions requirements. So we
> check arch_get_dma_bitsize's return value before set lowmem_bitsize.
> Avoid setting lowmem_bitsize to 0 by mistake.
In general, we want to avoid breaking bisection within a series. This 
means that this patch should be before patch #4.
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> Signed-off-by: Hongda Deng <Hongda.Deng@xxxxxxx>
> ---
>   xen/arch/arm/domain_build.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 6c86d52781..cf341f349f 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -265,9 +265,18 @@ static void __init allocate_memory_11(struct domain *d,
>       int i;
>   
>       bool lowmem = true;
> -    unsigned int lowmem_bitsize = min(32U, arch_get_dma_bitsize());
> +    unsigned int lowmem_bitsize = arch_get_dma_bitsize();
>       unsigned int bits;
>   
> +    /*
> +       When dma_bitsize and platform->dma_bitsize are not set,
> +       arch_get_dma_bitsize will return 0. That means this system
> +       doesn't need to reserve memory for DMA. But in order to
> +       meet above requirements, we still need to try to allocate
> +       memory below 4GB for Dom0.
> +    */
The coding style for comments is:

/*
 * A
 * B
 */

> +    lowmem_bitsize = lowmem_bitsize ? min(32U, lowmem_bitsize) : 32U;
> +
>       /*
>        * TODO: Implement memory bank allocation when DOM0 is not direct
>        * mapped
Cheers,

--
Julien Grall