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

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Date:	Thu, 17 Apr 2008 02:51:46 -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.
>
>  What happens when someone next comes to use that msi interrupt is
>  a reasonable question.
>
>  The PCI standard describes the state the bits in the msi capability
>  are supposed to be in after reset, and if a driver is going to
>  assume some state that is the only reasonable state for a driver to
>  expect the hardware to be in.  So we don't need to perform a
>  save/restore cycle.
>
>  Could you look at having pci_disable_msi reset the mask bit
>  to it's default state after we have called msi_set_enable(dev, 0)?
>  Once the msi capability is disabled the mask bit has no affect.

but the next kernel (RHEL 5.1) only can enable msi, and it doesn't
touch mask_bits (that is leaved as 0xff by first 2.6.25-rc2 later)
so device (nvidia mcp55 nic) doesn't work. --- if i manually used
setpci to set 0x60 to 0xfe or 0x00. it will work. also if i booted
kernel (RHEL 5.1), that 0x60
is always 0x00, even nic works with MSI.

YH
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