linux-kernel - Re: [PATCH 2/3] PCI: aardvark: Fix masking MSI interrupts

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Date:   Sun, 15 Aug 2021 22:55:01 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Pali Rohár <pali@...nel.org>
CC:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Marek Behún <kabel@...nel.org>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] PCI: aardvark: Fix masking MSI interrupts



On 15 August 2021 18:36:59 BST, "Pali Rohár" <pali@...nel.org> wrote:
>On Sunday 15 August 2021 17:56:04 Marc Zyngier wrote:
>> On Sun, 15 Aug 2021 11:36:23 +0100,
>> Pali Rohár <pali@...nel.org> wrote:
>> > 
>> > Masking of individual MSI interrupts is done via PCIE_MSI_MASK_REG
>> > register. At the driver probe time mask all MSI interrupts and then let
>> > kernel IRQ chip code to unmask particular MSI interrupt when needed.
>> > 
>> > Signed-off-by: Pali Rohár <pali@...nel.org>
>> > Cc: stable@...r.kernel.org # f21a8b1b6837 ("PCI: aardvark: Move to MSI handling using generic MSI support")
>> > ---
>> >  drivers/pci/controller/pci-aardvark.c | 44 ++++++++++++++++++++++++---
>> >  1 file changed, 40 insertions(+), 4 deletions(-)
>> > 
>> > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
>> > index bacfccee44fe..96580e1e4539 100644
>> > --- a/drivers/pci/controller/pci-aardvark.c
>> > +++ b/drivers/pci/controller/pci-aardvark.c
>> > @@ -480,12 +480,10 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
>> >  	advk_writel(pcie, PCIE_ISR1_ALL_MASK, PCIE_ISR1_REG);
>> >  	advk_writel(pcie, PCIE_IRQ_ALL_MASK, HOST_CTRL_INT_STATUS_REG);
>> >  
>> > -	/* Disable All ISR0/1 Sources */
>> > +	/* Disable All ISR0/1 and MSI Sources */
>> >  	advk_writel(pcie, PCIE_ISR0_ALL_MASK, PCIE_ISR0_MASK_REG);
>> >  	advk_writel(pcie, PCIE_ISR1_ALL_MASK, PCIE_ISR1_MASK_REG);
>> > -
>> > -	/* Unmask all MSIs */
>> > -	advk_writel(pcie, ~(u32)PCIE_MSI_ALL_MASK, PCIE_MSI_MASK_REG);
>> > +	advk_writel(pcie, PCIE_MSI_ALL_MASK, PCIE_MSI_MASK_REG);
>> >  
>> >  	/* Unmask summary MSI interrupt */
>> >  	reg = advk_readl(pcie, PCIE_ISR0_MASK_REG);
>> > @@ -1026,6 +1024,40 @@ static int advk_msi_set_affinity(struct irq_data *irq_data,
>> >  	return -EINVAL;
>> >  }
>> >  
>> > +static void advk_msi_irq_mask(struct irq_data *d)
>> > +{
>> > +	struct advk_pcie *pcie = d->domain->host_data;
>> > +	irq_hw_number_t hwirq = irqd_to_hwirq(d);
>> > +	u32 mask;
>> > +
>> > +	mask = advk_readl(pcie, PCIE_MSI_MASK_REG);
>> > +	mask |= BIT(hwirq);
>> > +	advk_writel(pcie, mask, PCIE_MSI_MASK_REG);
>> 
>> This isn't atomic, and will results in corruption when two MSIs are
>> masked/unmasked concurrently.
>
>Does it mean that also current implementation of masking legacy
>interrupt is incorrect?
>
>https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/controller/pci-aardvark.c?h=v5.13#n874

Yes, that's completely busted. If you have configuration registers that are shared between interrupts and that the HW doesn't provide set/clear accessors so that it can cope with such races, you need mutual exclusion.

You'd think people would have worked that one out.... 60 years ago?

        M.

Jazz is not dead, it just smells funny