Re: [Xen-devel] [PATCH V4] xen/arm: domain_build: allocate lowmem for dom0 as much as possible

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 1 Nov 2016, Julien Grall wrote:
> Hi Peng,
> 
> Sorry for the late answer.
> 
> On 23/09/2016 03:55, Peng Fan wrote:
> > On AArch64 SoCs, some IPs may only have the capability to access
> > 32 bits address space. The physical memory assigned for Dom0 maybe
> > not in 4GB address space, then the IPs will not work properly.
> > So need to allocate memory under 4GB for Dom0.
> > 
> > There is no restriction that how much lowmem needs to be allocated for
> > Dom0 ,so allocate lowmem as much as possible for Dom0.
> > 
> > This patch does not affect 32-bit domain, because Variable "lowmem" is
> > set to true at the beginning. If failed to allocate bank0 under 4GB,
> > need to panic for 32-bit domain, because 32-bit domain requires bank0
> > be allocated under 4GB.
> > 
> > For 64-bit domain, set "lowmem" to false, and continue allocating
> > memory from above 4GB.
> > 
> > Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
> > Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > Cc: Julien Grall <julien.grall@xxxxxxx>
> 
> Reviewed-by: Julien Grall <julien.grall@xxxxxxx>
> 
> I am undecided whether this should be considered as a bug fix for Xen 4.8. Are
> you aware of any ARM64 platform we currently support requiring allocation of
> memory below 4GB?

I am more comfortable having this in 4.9 (I queued it up in xen-arm-next
for now), unless we have a regression, a concrete problem, with an
existing supported platform, like you wrote.

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