Re: [PATCH 2/2] x86/PCI: limit the size of the 64bit window to 256GB v2

From: Bjorn Helgaas
Date: Wed Jan 10 2018 - 13:02:38 EST


[+cc linux-pci, previous cc list]

On Wed, Jan 10, 2018 at 01:25:51PM +0100, Christian König wrote:
> Avoid problems with BIOS implementations which don't report all used
> resources to the OS by only allocating a 256GB window directly below the
> hardware limit.
>
> v2: cleanup code a bit more, update comment and explain the hw limit

Fixes a silent reboot loop reported by Aaro Koskinen
<aaro.koskinen@xxxxxx> on an AMD-based MSI MS-7699/760GA-P43(FX)
system.

Link: https://lkml.kernel.org/r/20180105220412.fzpwqe4zljdawr36@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: Aaro Koskinen <aaro.koskinen@xxxxxx>

> Signed-off-by: Christian König <christian.koenig@xxxxxxx>
> ---
> arch/x86/pci/fixup.c | 19 +++++++++----------
> 1 file changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/pci/fixup.c b/arch/x86/pci/fixup.c
> index a91280da2ea1..9c1c98d7e3a7 100644
> --- a/arch/x86/pci/fixup.c
> +++ b/arch/x86/pci/fixup.c
> @@ -662,10 +662,11 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_INTEL, 0x2033, quirk_no_aersid);
> */
> static void pci_amd_enable_64bit_bar(struct pci_dev *dev)
> {
> - unsigned i;
> u32 base, limit, high;
> - struct resource *res, *conflict;
> struct pci_dev *other;
> + struct resource *res;
> + unsigned i;
> + int r;
>
> if (!(pci_probe & PCI_BIG_ROOT_WINDOW))
> return;
> @@ -702,19 +703,17 @@ static void pci_amd_enable_64bit_bar(struct pci_dev *dev)
> if (!res)
> return;
>
> + /* Allocate a 256GB window directly below the 0xfd00000000 hw limit */

Can you include a citation for the hardware limit in the changelog?
I'll try to dig it up myself if you don't beat me to it.

> res->name = "PCI Bus 0000:00";
> res->flags = IORESOURCE_PREFETCH | IORESOURCE_MEM |
> IORESOURCE_MEM_64 | IORESOURCE_WINDOW;
> - res->start = 0x100000000ull;
> + res->start = 0xbd00000000ull;
> res->end = 0xfd00000000ull - 1;
>
> - /* Just grab the free area behind system memory for this */
> - while ((conflict = request_resource_conflict(&iomem_resource, res))) {
> - if (conflict->end >= res->end) {
> - kfree(res);
> - return;
> - }
> - res->start = conflict->end + 1;
> + r = request_resource(&iomem_resource, res);
> + if (r) {
> + kfree(res);
> + return;
> }
>
> dev_info(&dev->dev, "adding root bus resource %pR\n", res);
> --
> 2.11.0
>