Re: [PATCH v8 10/15] octeontx2-af: Reconfig MSIX base with IOVA

On Tue, Oct 9, 2018 at 11:20 AM Sunil Kovvuri [off-list ref] wrote:

On Tue, Oct 9, 2018 at 1:27 PM Arnd Bergmann [off-list ref] wrote:

quoted

On Tue, Oct 9, 2018 at 9:03 AM Sunil Kovvuri [off-list ref] wrote:

quoted

On Mon, Oct 8, 2018 at 5:38 PM Arnd Bergmann [off-list ref] wrote:

quoted

On Sun, Oct 7, 2018 at 5:01 PM [off-list ref] wrote:

I think if you enable CONFIG_DEBUG_VIRTUAL, the virt_to_page()
above should trigger a warning in

phys_addr_t __virt_to_phys(unsigned long x)
{
        WARN(!__is_lm_address(x),
             "virt_to_phys used for non-linear address: %pK (%pS)\n",
              (void *)x,
              (void *)x);

        return __virt_to_phys_nodebug(x);
}

Can you verify that?

        Arnd

No, it isn't, as for 64bit systems CONFIG_SPARSEMEM_VMEMMAP is enabled.

But that is also user-selectable, right? It still seems to be really
fragile to rely on non-documented behavior of virt_to_phys()
here, if that only works for some configurations.

But is there any alternative to what is being done ?

I'm not completely sure, but there may be a way to do this correctly
using the iommu API instead of the dma-mapping API. What you do
here is fairly rare, but not unprecedented.

      Arnd