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    SubjectRe: [for-next PATCH 4/5] RDMA/rxe: refactor iova_to_vaddr
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    On lunedì 21 novembre 2022 19:53:54 CET Jason Gunthorpe wrote:
    > On Wed, Nov 16, 2022 at 01:37:14PM +0100, Fabio M. De Francesco wrote:
    > > > - return (void *)(uintptr_t)mr->map[m]->buf[n].addr + offset;
    > > > + if (mr->ibmr.type == IB_MR_TYPE_USER) {
    > > > + char *paddr;
    > > > + struct page *pg = mr->map[m]->buf[n].page;
    > > > +
    > > > + paddr = kmap_local_page(pg);
    > > > + if (paddr == NULL) {
    > > > + pr_warn("Failed to map page");
    > > > + return NULL;
    > > > + }
    > >
    > > I know nothing about this code but I am here as a result of regular checks
    > > for changes to HIGHMEM mappings across the entire kernel. So please
    forgive
    > > me if I'm objecting to the correct changes.
    > >
    > > 1) It looks like this code had a call to page_address() and you converted
    it
    > > to mapping with kmap_local_page().
    >
    > It only worked properly because the kconfig is blocking CONFIG_HIGHMEM
    > so ZONE_HIGHMEM doesn't exist. These pages are obtained from GUP and
    > could be anything.
    >
    > This is done indirectly through
    >
    > config INFINIBAND_VIRT_DMA
    > def_bool !HIGHMEM
    > But this patch is undoing parts of what are causing that restriction
    > by using the proper APIs. Though I'm not sure if we can eventually get
    > to remove it for RXE completely.
    > Jason

    Ah, OK. This code was for !HIGHMEM kernels...

    I understand but, FWIW I doubt that the use of page_address(), instead of
    kmapping, should ever be made on the bases that kconfig is blocking HIGHMEM.

    However, if I understand correctly, that restriction (!HIGHMEM) is going to be
    removed. Therefore, page_address() will break on HIGHMEM and Jason is
    correctly converting to kmap_local_page().

    There is only one thing left... I think that he missed another mail from me.
    The one you responded to was missing the final paragraph, so I sent another
    message few minutes later.

    kmap_local_page() returns always valid pointers to kernel virtual addresses. I
    can't see any ways for kmap_local_page() to return NULL. Therefore, I was
    asking for the reason to check for NULL.

    Thanks,

    Fabio



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