On Fri, Jul 26, 2019 at 12:55:03PM +0000, Nicholas Johnson wrote: > Background > ========================================================================== I don't think the above are needed. > Currently, the kernel can sometimes assign the MMIO_PREF window > additional size into the MMIO window, resulting in double the MMIO > additional size, even if the MMIO_PREF window was successful. > > This happens if in the first pass, the MMIO_PREF succeeds but the MMIO > fails. In the next pass, because MMIO_PREF is already assigned, the > attempt to assign MMIO_PREF returns an error code instead of success > (nothing more to do, already allocated). > > Example of problem (more context can be found in the bug report URL): Maybe add bit more context in the changelog. Also explain how the problem can be reproduced. > Mainline kernel: > pci 0000:06:01.0: BAR 14: assigned [mem 0x90100000-0xa00fffff] = 256M > pci 0000:06:04.0: BAR 14: assigned [mem 0xa0200000-0xb01fffff] = 256M > > Patched kernel: > pci 0000:06:01.0: BAR 14: assigned [mem 0x90100000-0x980fffff] = 128M > pci 0000:06:04.0: BAR 14: assigned [mem 0x98200000-0xa01fffff] = 128M > > This was using pci=realloc,hpmemsize=128M,nocrs - on the same machine > with the same configuration, with a Ubuntu mainline kernel and a kernel > patched with this patch series. > > This patch is vital for the next patch in the series. The next patch There is no next patch in the patch series ;-) > allows the user to specify MMIO and MMIO_PREF independently. If the > MMIO_PREF is set to be very large, this bug will end up more than > doubling the MMIO size. The bug results in the MMIO_PREF being added to > the MMIO window, which means doubling if MMIO_PREF size == MMIO size. > With a large MMIO_PREF, without this patch, the MMIO window will likely > fail to be assigned altogether due to lack of 32-bit address space. > > Patch notes > ========================================================================== Here also the above two lines are not needed. > Change find_free_bus_resource() to not skip assigned resources with > non-null parent. > > Add checks in pbus_size_io() and pbus_size_mem() to return success if > resource returned from find_free_bus_resource() is already allocated. > > This avoids pbus_size_io() and pbus_size_mem() returning error code to > __pci_bus_size_bridges() when a resource has been successfully assigned > in a previous pass. This fixes the existing behaviour where space for a > resource could be reserved multiple times in different parent bridge > windows. This also greatly reduces the number of failed BAR messages in > dmesg when Linux assigns resources. > > See related from Logan Gunthorpe (same problem, different solution): > https://lore.kernel.org/lkml/20190531171216.20532-2-logang@xxxxxxxxxxxx/T/#u Link: https://lore.kernel.org/lkml/20190531171216.20532-2-logang@xxxxxxxxxxxx/T/#u > Solves bug report: https://bugzilla.kernel.org/show_bug.cgi?id=203243 Link: https://bugzilla.kernel.org/show_bug.cgi?id=203243 The patch itself looks good to me.
