linux-kernel - Re: [PATCH] PCI: apple: Initialize pcie->nvecs before using it

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Date:   Sat, 11 Mar 2023 14:34:39 +0000
From:   alyssa@...enzweig.io
To:     "Sven Peter" <sven@...npeter.dev>, "Marc Zyngier" <maz@...nel.org>
Cc:     "Lorenzo Pieralisi" <lpieralisi@...nel.org>,
        "Krzysztof Wilczyński" <kw@...ux.com>,
        "Rob Herring" <robh@...nel.org>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        asahi@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: apple: Initialize pcie->nvecs before using it

Whoops!

Reviewed-by: Alyssa Rosenzweig <alyssa@...enzweig.io>

March 11, 2023 8:34 AM, "Sven Peter" <sven@...npeter.dev> wrote:

> apple_pcie_setup_port computes ilog2(pcie->nvecs) to setup the number of
> MSIs available for each port. It is however called before apple_msi_init
> which actually initializes pcie->nvecs.
> Luckily, pcie->nvecs is part of kzalloc-ed structure and thus
> initialized as zero. ilog2(0) happens to be 0xffffffff which then just
> configures more MSIs in hardware than we actually have. This doesn't
> break anything because we never hand out those vectors.
> Let's swap the order of the two calls so that we use the correctly
> initialized value.
> 
> Fixes: 476c41ed4597 ("PCI: apple: Implement MSI support")
> Signed-off-by: Sven Peter <sven@...npeter.dev>
> ---
> drivers/pci/controller/pcie-apple.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c
> index 66f37e403a09..8b7b084cf287 100644
> --- a/drivers/pci/controller/pcie-apple.c
> +++ b/drivers/pci/controller/pcie-apple.c
> @@ -783,6 +783,10 @@ static int apple_pcie_init(struct pci_config_window *cfg)
> cfg->priv = pcie;
> INIT_LIST_HEAD(&pcie->ports);
> 
> + ret = apple_msi_init(pcie);
> + if (ret)
> + return ret;
> +
> for_each_child_of_node(dev->of_node, of_port) {
> ret = apple_pcie_setup_port(pcie, of_port);
> if (ret) {
> @@ -792,7 +796,7 @@ static int apple_pcie_init(struct pci_config_window *cfg)
> }
> }
> 
> - return apple_msi_init(pcie);
> + return 0;
> }
> 
> static int apple_pcie_probe(struct platform_device *pdev)
> -- 
> 2.25.1