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

[Peng Fan]

Hi Stefano,

> Subject: RE: [PATCH] arm: xen: mm: use __GPF_DMA32 for arm64
> 
> On Wed, 28 Aug 2019, Peng Fan wrote:
> > 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.
> 
> Hi Peng,
> 
> Sorry for being so late in replying, this email got lost in the noise.
> 
> 
> > > > Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
> > > > ---
> > > >   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;
> >                 }
> >         }
> 
> Yes I think this is the way to go, but we are trying not to add any #ifdef
> CONFIG_ARM64 under arch/arm. Maybe you could introduce a static inline
> function to set GFP_DMA:
> 
>   static inline void xen_set_gfp_dma(gfp_t *flags)
> 
> it could be implemented under arch/arm/include/asm/xen/page.h for arm
> and under arch/arm64/include/asm/xen/page.h for arm64 using __GFP_DMA
> for the former and __GFP_DMA32 for the latter.

Thanks for your suggestion. I'll use this in V2.

Thanks,
Peng.