RE: [PATCH] arm: xen: mm: use __GPF_DMA32 for arm64

[Peng Fan]

Hi Robin,

> Subject: Re: [PATCH] arm: xen: mm: use __GPF_DMA32 for arm64
> 
> On 09/07/2019 09:22, Peng Fan wrote:
> > arm64 shares some code under arch/arm/xen, including mm.c.
> > However ZONE_DMA is removed by commit
> > ad67f5a6545("arm64: replace ZONE_DMA with ZONE_DMA32").
> > So to ARM64, need use __GFP_DMA32.
> >
> > Signed-off-by: Peng Fan <peng....@nxp.com>
> > ---
> >   arch/arm/xen/mm.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c index
> > e1d44b903dfc..a95e76d18bf9 100644
> > --- a/arch/arm/xen/mm.c
> > +++ b/arch/arm/xen/mm.c
> > @@ -27,7 +27,7 @@ unsigned long xen_get_swiotlb_free_pages(unsigned
> > int order)
> >
> >     for_each_memblock(memory, reg) {
> >             if (reg->base < (phys_addr_t)0xffffffff) {
> > -                   flags |= __GFP_DMA;
> > +                   flags |= __GFP_DMA | __GFP_DMA32;
> 
> Given the definition of GFP_ZONE_BAD, I'm not sure this combination of flags
> is strictly valid, but rather is implicitly reliant on only one of those 
> zones ever
> actually existing. As such, it seems liable to blow up if the plans to add
> ZONE_DMA to arm64[1] go ahead.

How about this, or do you have any suggestions?
diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
index d33b77e9add3..f61c29a4430f 100644
--- a/arch/arm/xen/mm.c
+++ b/arch/arm/xen/mm.c
@@ -28,7 +28,11 @@ unsigned long xen_get_swiotlb_free_pages(unsigned int order)

        for_each_memblock(memory, reg) {
                if (reg->base < (phys_addr_t)0xffffffff) {
+#ifdef CONFIG_ARM64
+                       flags |= __GFP_DMA32;
+#else
                        flags |= __GFP_DMA;
+#endif
                        break;
                }
        }

Thanks,
Peng.

> 
> Robin.
> 
> [1]
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ke
> rnel.org%2Flinux-arm-kernel%2F20190820145821.27214-1-nsaenzjulienne%
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> >                     break;
> >             }
> >     }
> >