Re: [Xen-devel] [PATCH V1] xen/arm: domain_build: introduce dom0_lowmem bootargs

["Edgar E. Iglesias" <edgar.iglesias@xxxxxxxxx>]

On Wed, Sep 14, 2016 at 08:40:09PM +0800, Peng Fan wrote:
> On Wed, Sep 14, 2016 at 01:34:10PM +0100, Julien Grall wrote:
> >
> >
> >On 14/09/16 13:18, Peng Fan wrote:
> >>Hello Julien,
> >>
> >>On Wed, Sep 14, 2016 at 01:06:01PM +0100, Julien Grall wrote:
> >>>
> >>>
> >>>On 14/09/16 13:03, Peng Fan wrote:
> >>>>Hello Julien,
> >>>
> >>>Hello Peng,
> >>>
> >>>>On Wed, Sep 14, 2016 at 11:47:10AM +0100, Julien Grall wrote:
> >>>>>Hello,
> >>>>>
> >>>>>On 14/09/16 08:41, Peng Fan wrote:
> >>>>>>On Wed, Sep 14, 2016 at 08:23:24AM +0100, Julien Grall wrote:
> >>>>>>diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> >>>>>>index 35ab08d..cc71e6f 100644
> >>>>>>--- a/xen/arch/arm/domain_build.c
> >>>>>>+++ b/xen/arch/arm/domain_build.c
> >>>>>>@@ -28,6 +28,8 @@
> >>>>>>
> >>>>>>static unsigned int __initdata opt_dom0_max_vcpus;
> >>>>>>integer_param("dom0_max_vcpus", opt_dom0_max_vcpus);
> >>>>>>+static bool_t __initdata opt_dom0_use_lowmem;
> >>>>>>+boolean_param("dom0_use_lowmem", opt_dom0_use_lowmem);
> >>>>>>
> >>>>>>int dom0_11_mapping = 1;
> >>>>>>
> >>>>>>@@ -244,7 +246,7 @@ static void allocate_memory(struct domain *d, struct
> >>>>>>kernel_info *kinfo)
> >>>>>>   unsigned int order = get_11_allocation_size(kinfo->unassigned_mem);
> >>>>>>   int i;
> >>>>>>        
> >>>>>>-    bool_t lowmem = is_32bit_domain(d);
> >>>>>>+    bool_t lowmem = is_32bit_domain(d) || opt_dom0_use_lowmem;
> >>>>>>   unsigned int bits;
> >>>>>>
> >>>>>>
> >>>>>>Pass "dom0_use_lowmem=1" to xen to allocate lowmem as much as possible.
> >>>>>
> >>>>>Again, what is the benefit to have a command line option for that?
> >>>>
> >>>>Then you prefer directly change "bool_t lowmem = is_32bit_domain(d);" to 
> >>>>"bool_t lowmem = true" ?
> >>>>I just want to give user a choice.
> >>>
> >>>We don't add new command line parameter just because they look cool to 
> >>>have.
> >>>So far, you did not explain why it would be good to let the choice to the
> >>>user and how it could be used.
> >>
> >>I have not try, if there is no lowmem.
> >>
> >>I have not look into alloc_domheap_pages.
> >>I am not sure whether there is such a platform or not,
> >>just thinking if there is soc that dram memory starts from 4GB, and there 
> >>is no dram
> >>below 4GB. If we still can get memory when lowmem is true, I am ok to 
> >>change directly assign
> >>lowmem with value true. Anyway I have not look into the internals of 
> >>domheap and
> >>not sure whether there is such a platform that no lowmem (:-
> >
> >We cannot exclude this possibility. However, the only reason that Xen is
> >requiring to allocate a bank below 4GB for 32-bit domain is to handle
> >non-LPAE kernel.
> 
> Now also need to handle device that have DMA limitation -:)

Hi Peng,

Doesn't your platform have an IOMMU/SMMU?

Cheers,
Edgar

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