Re: [PATCH] RISC-V: Fix FIXMAP area corruption on RV32 systems
From: Anup Patel
Date: Mon Aug 19 2019 - 00:49:17 EST
On Sun, Aug 18, 2019 at 11:49 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> > +#define FIXADDR_TOP (VMALLOC_START)
> Nit: no need for the braces, the definitions below don't use it
Sure, I will update and send v2 soon.
> > +#ifdef CONFIG_64BIT
> > +#define FIXADDR_SIZE PMD_SIZE
> > +#else
> > +#define FIXADDR_SIZE PGDIR_SIZE
> > +#endif
> > +#define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE)
> > +
> > /*
> > - * Task size is 0x4000000000 for RV64 or 0xb800000 for RV32.
> > + * Task size is 0x4000000000 for RV64 or 0x9fc00000 for RV32.
> > * Note that PGDIR_SIZE must evenly divide TASK_SIZE.
> > */
> > #ifdef CONFIG_64BIT
> > #define TASK_SIZE (PGDIR_SIZE * PTRS_PER_PGD / 2)
> > #else
> > -#define TASK_SIZE VMALLOC_START
> > +#define TASK_SIZE FIXADDR_START
> > #endif
> Mentioning the addresses is a little weird. IMHO this would be
> a much nicer place to explain the high-level memory layout, including
> maybe a little ASCII art. Also we could have one #ifdef CONFIG_64BIT
> for both related values. Last but not least instead of saying that
> something should be dividable it would be nice to have a BUILD_BUG_ON
> to enforce it.
> Either way we are late in the cycle, so I guess this is ok for now:
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> But I'd love to see this area improved a little further as it is full
> of mine fields.
I agree with you. We also have Sparsemem and KASAN patches which
touch virtual memory layout so it's important to have virtual memory layout
documented clearly. I can add the required documentation as separate patch.
I think the best place to add ASCII art would be asm/pgtable.h where all
virtual memory related defines are placed. Suggestions??