linux-kernel - Re: [PATCH] PCI: Release coalesced resource

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Message-ID: <DM6PR03MB53729AA409FA1DC12ABCBCDEF04DA@DM6PR03MB5372.namprd03.prod.outlook.com>
Date:   Mon, 5 Jun 2023 08:44:43 +0000
From:   Ross Lagerwall <ross.lagerwall@...rix.com>
To:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
CC:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI: Release coalesced resource

> From: Ross Lagerwall <ross.lagerwall@...rix.com>
> Sent: Thursday, May 25, 2023 4:32 PM
> To: linux-pci@...r.kernel.org <linux-pci@...r.kernel.org>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>; Kai-Heng Feng <kai.heng.feng@...onical.com>; linux-kernel@...r.kernel.org <linux-kernel@...r.kernel.org>; Ross Lagerwall <ross.lagerwall@...rix.com>
> Subject: [PATCH] PCI: Release coalesced resource 
>  
> When contiguous windows are coalesced, the resource is invalidated and
> consequently not added to the bus. However, it remains in the resource
> hierarchy:
> 
> ...
>   ef2fff00-ef2fffff : 0000:00:13.2
>     ef2fff00-ef2fffff : ehci_hcd
> 00000000-00000000 : PCI Bus 0000:00
> f0000000-f3ffffff : PCI MMCONFIG 0000 [bus 00-3f]
>   f0000000-f3ffffff : Reserved
> ...
> 
> In some cases (e.g. the Xen scratch region), this causes future calls to
> allocate_resource() to choose an inappropriate location which the caller
> cannot handle. Fix by releasing the resource and removing from the
> hierarchy.
> 
> Fixes: 7c3855c423b1 ("PCI: Coalesce host bridge contiguous apertures")
> Signed-off-by: Ross Lagerwall <ross.lagerwall@...rix.com>
> ---
>  drivers/pci/probe.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 0b2826c4a832..00ed20ac0dd6 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -997,8 +997,10 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge)
>          resource_list_for_each_entry_safe(window, n, &resources) {
>                  offset = window->offset;
>                  res = window->res;
> -               if (!res->flags && !res->start && !res->end)
> +               if (!res->flags && !res->start && !res->end) {
> +                       release_resource(res);
>                          continue;
> +               }
>  
>                  list_move_tail(&window->node, &bridge->windows);
>  
> -- 
> 2.31.1

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