Re: [PATCH] x86_64: restore mask_bits in msi shutdown

From: Yinghai Lu
Date: Thu Apr 17 2008 - 06:05:20 EST


On Thu, Apr 17, 2008 at 2:19 AM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:
>
> Yinghai Lu <yhlu.kernel.send@xxxxxxxxx> writes:
>
> > I can not kexec RHEL 5.1 from 2.6.25-rc3 later
> >
> > caused by:
> > commit 89d694b9dbe769ca1004e01db0ca43964806a611
> > Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Date: Mon Feb 18 18:25:17 2008 +0100
> >
> > genirq: do not leave interupts enabled on free_irq
> >
> > The default_disable() function was changed in commit:
> >
> > 76d2160147f43f982dfe881404cfde9fd0a9da21
> > genirq: do not mask interrupts by default
> >
> > It removed the mask function in favour of the default delayed
> > interrupt disabling. Unfortunately this also broke the shutdown in
> > free_irq() when the last handler is removed from the interrupt for
> > those architectures which rely on the default implementations. Now we
> > can end up with a enabled interrupt line after the last handler was
> > removed, which can result in spurious interrupts.
> >
> > Fix this by adding a default_shutdown function, which is only
> > installed, when the irqchip implementation does provide neither a
> > shutdown nor a disable function.
> >
> > [@stable: affected versions: .21 - .24 ]
> >
> >
> >
> > for MSI, default_shutdown will call mask_bit for msi device. so all mask bits
> > will
> > left disabled after free_irq.
> > then if kexec next kernel that only can use msi_enable bit.
> > all device's MSI can not be used.
> >
> > So try to restore MSI mask bits that is saved before using msi in first kernel.
> >
> > Signed-off-by: Yinghai Lu <yhlu.kernel@xxxxxxxxx>
>
> Ouch! In the case of MSI-X this is horrible. Reenabling an interrupt
> line when we are not using it. That is likely to cause even stranger
> things than kexec to fail.

only does save and restore with msi and doesn't do anything with MSIX

+void msi_restore_mask_bits(unsigned int irq)
+{
+ struct msi_desc *entry;
+
+ entry = get_irq_msi(irq);
+ BUG_ON(!entry || !entry->dev);
+ switch (entry->msi_attrib.type) {
+ case PCI_CAP_ID_MSI:
+ if (entry->msi_attrib.maskbit) {
+ int pos;
+ u32 mask_bits;
+
+ pos = (long)entry->mask_base;
+ mask_bits = entry->orig_mask_bits;
+ pci_write_config_dword(entry->dev, pos, mask_bits);
+ }
+ break;
+ case PCI_CAP_ID_MSIX:
+ break; ======================> does not restore that for MSIX
+ default:
+ BUG();
+ break;
+ }
+}

YH
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