linux-kernel - Re: [PATCH v3 1/1] PCI: Fix bug resulting in double hpmemsize being assigned to MMIO window

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Message-ID: <7f824f5f-ee0f-0591-9170-1433c0813857@deltatee.com>
Date:   Wed, 13 Nov 2019 09:50:50 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "corbet@....net" <corbet@....net>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>
Subject: Re: [PATCH v3 1/1] PCI: Fix bug resulting in double hpmemsize being
 assigned to MMIO window



On 2019-11-13 8:25 a.m., Nicholas Johnson wrote:
> Currently, the kernel can sometimes assign the MMIO_PREF window
> additional size into the MMIO window, resulting in extra MMIO additional
> size, despite the MMIO_PREF additional size being assigned successfully
> into the MMIO_PREF window.
> 
> 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). Hence, the size which is
> actually allocated, but thought to have failed, is placed in the MMIO
> window.
> 
> Example of problem (more context can be found in the bug report URL):
> 
> 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.
> 
> 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,
> the MMIO window will likely fail to be assigned altogether due to lack
> of 32-bit address space.
> 
> Change find_free_bus_resource() to do the following:
> - Return first unassigned resource of the correct type.
> - If none of the above, return first assigned resource of the correct type.
> - If none of the above, return NULL.
> 
> Returning an assigned resource of the correct type allows the caller to
> distinguish between already assigned and no resource of the correct type.
> 
> Rename find_free_bus_resource to find_bus_resource_of_type().
> 
> 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.
> 
> Link: https://lore.kernel.org/lkml/20190531171216.20532-2-logang@deltatee.com/T/#u
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=203243
> 
> Reported-by: Kit Chow <kchow@...aio.com>
> Reported-by: Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
> Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
> Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>

You can add mine as well:

Reviewed-by: Logan Gunthorpe <logang@...tatee.com>

Thanks,

Logan