linux-kernel - Re: [PATCH] x86_64: restore mask

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Message-ID: <86802c440804170244g3463d1bcx632844dc0204ded2@mail.gmail.com>
Date:	Thu, 17 Apr 2008 02:44:16 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	hlu.kernel@...il.com, "Thomas Gleixner" <tglx@...utronix.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Ingo Molnar" <mingo@...e.hu>, "Jeff Garzik" <jeff@...zik.org>,
	"Ayaz Abdulla" <aabdulla@...dia.com>,
	"kernel list" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86_64: restore mask_bits in msi shutdown

On Thu, Apr 17, 2008 at 2:19 AM, Eric W. Biederman
<ebiederm@...ssion.com> wrote:
>
> Yinghai Lu <yhlu.kernel.send@...il.com> writes:
>
>  > I can not kexec RHEL 5.1 from 2.6.25-rc3 later
>  >
>  > caused by:
>  > commit 89d694b9dbe769ca1004e01db0ca43964806a611
>  > Author: Thomas Gleixner <tglx@...utronix.de>
>  > 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@...il.com>
>
>  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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