Re: [PATCH v13 01/12] swiotlb: Refactor swiotlb init functions

[Claire Chang <tientzu@chromium.org>]

On Fri, Jun 18, 2021 at 7:30 AM Stefano Stabellini
<sstabellini@kernel.org> wrote:
>
> On Thu, 17 Jun 2021, Claire Chang wrote:
> > Add a new function, swiotlb_init_io_tlb_mem, for the io_tlb_mem struct
> > initialization to make the code reusable.
> >
> > Signed-off-by: Claire Chang <tientzu@chromium.org>
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > Tested-by: Stefano Stabellini <sstabellini@kernel.org>
> > Tested-by: Will Deacon <will@kernel.org>
> > ---
> >  kernel/dma/swiotlb.c | 50 ++++++++++++++++++++++----------------------
> >  1 file changed, 25 insertions(+), 25 deletions(-)
> >
> > diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> > index 52e2ac526757..47bb2a766798 100644
> > --- a/kernel/dma/swiotlb.c
> > +++ b/kernel/dma/swiotlb.c
> > @@ -168,9 +168,28 @@ void __init swiotlb_update_mem_attributes(void)
> >       memset(vaddr, 0, bytes);
> >  }
> >
> > -int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
> > +static void swiotlb_init_io_tlb_mem(struct io_tlb_mem *mem, phys_addr_t start,
> > +                                 unsigned long nslabs, bool late_alloc)
> >  {
> > +     void *vaddr = phys_to_virt(start);
> >       unsigned long bytes = nslabs << IO_TLB_SHIFT, i;
> > +
> > +     mem->nslabs = nslabs;
> > +     mem->start = start;
> > +     mem->end = mem->start + bytes;
> > +     mem->index = 0;
> > +     mem->late_alloc = late_alloc;
> > +     spin_lock_init(&mem->lock);
> > +     for (i = 0; i < mem->nslabs; i++) {
> > +             mem->slots[i].list = IO_TLB_SEGSIZE - io_tlb_offset(i);
> > +             mem->slots[i].orig_addr = INVALID_PHYS_ADDR;
> > +             mem->slots[i].alloc_size = 0;
> > +     }
> > +     memset(vaddr, 0, bytes);
> > +}
> > +
> > +int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
> > +{
> >       struct io_tlb_mem *mem;
> >       size_t alloc_size;
> >
> > @@ -186,16 +205,8 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
> >       if (!mem)
> >               panic("%s: Failed to allocate %zu bytes align=0x%lx\n",
> >                     __func__, alloc_size, PAGE_SIZE);
> > -     mem->nslabs = nslabs;
> > -     mem->start = __pa(tlb);
> > -     mem->end = mem->start + bytes;
> > -     mem->index = 0;
> > -     spin_lock_init(&mem->lock);
> > -     for (i = 0; i < mem->nslabs; i++) {
> > -             mem->slots[i].list = IO_TLB_SEGSIZE - io_tlb_offset(i);
> > -             mem->slots[i].orig_addr = INVALID_PHYS_ADDR;
> > -             mem->slots[i].alloc_size = 0;
> > -     }
> > +
> > +     swiotlb_init_io_tlb_mem(mem, __pa(tlb), nslabs, false);
> >
> >       io_tlb_default_mem = mem;
> >       if (verbose)
> > @@ -282,8 +293,8 @@ swiotlb_late_init_with_default_size(size_t default_size)
> >  int
> >  swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
> >  {
> > -     unsigned long bytes = nslabs << IO_TLB_SHIFT, i;
> >       struct io_tlb_mem *mem;
> > +     unsigned long bytes = nslabs << IO_TLB_SHIFT;
> >
> >       if (swiotlb_force == SWIOTLB_NO_FORCE)
> >               return 0;
> > @@ -297,20 +308,9 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs)
> >       if (!mem)
> >               return -ENOMEM;
> >
> > -     mem->nslabs = nslabs;
> > -     mem->start = virt_to_phys(tlb);
> > -     mem->end = mem->start + bytes;
> > -     mem->index = 0;
> > -     mem->late_alloc = 1;
> > -     spin_lock_init(&mem->lock);
> > -     for (i = 0; i < mem->nslabs; i++) {
> > -             mem->slots[i].list = IO_TLB_SEGSIZE - io_tlb_offset(i);
> > -             mem->slots[i].orig_addr = INVALID_PHYS_ADDR;
> > -             mem->slots[i].alloc_size = 0;
> > -     }
> > -
> > +     memset(mem, 0, sizeof(*mem));
> > +     swiotlb_init_io_tlb_mem(mem, virt_to_phys(tlb), nslabs, true);
> >       set_memory_decrypted((unsigned long)tlb, bytes >> PAGE_SHIFT);
> > -     memset(tlb, 0, bytes);
>
> This is good for swiotlb_late_init_with_tbl. However I have just noticed
> that mem could also be allocated from swiotlb_init_with_tbl, in which
> case the zeroing is missing. I think we need another memset in
> swiotlb_init_with_tbl as well. Or maybe it could be better to have a
> single memset at the beginning of swiotlb_init_io_tlb_mem instead. Up to
> you.

swiotlb_init_with_tbl uses memblock_alloc to allocate the io_tlb_mem
and memblock_alloc[1] will do memset in memblock_alloc_try_nid[2], so
swiotlb_init_with_tbl is also good.
I'm happy to add the memset in swiotlb_init_io_tlb_mem if you think
it's clearer and safer.

[1] https://elixir.bootlin.com/linux/v5.13-rc6/source/include/linux/memblock.h#L407
[2] https://elixir.bootlin.com/linux/v5.13-rc6/source/mm/memblock.c#L1555