Michael S. Tsirkin wrote:
On Mon, May 18, 2009 at 03:33:20PM +0300, Avi Kivity wrote:
Michael S. Tsirkin wrote:
On the other hand, in MSI-X mask bit is mandatory, not optional
so we'll have to support it for assigned devices at some point.
If we are worried about speed of masking/unmasking MSI-X interrupts for
assigned devices (older kernels used to mask them, recent kernels leave
this to drivers) we will probably need to have MSI-X support in the
kernel, and have kernel examine the mask bit before injecting the
interrupt, just like real devices do.
Yes.
Actually, if we do that, we'll need to address a race where a driver
has updated the mask bit in the window after we tested it
and before we inject the interrupt. Not sure how to do this.
The driver can't tell if the interrupt came first, so it's a valid race
(real hardware has the same race).
The driver for real device can do a read followed by sync_irq to flush
out interrupts.
If it generates the interrupt after masking it in the msi-x entry, we'll
see it. If it generates the interrupt before masking it, it may or may
not receive the interrupt, even on real hardware.
--
error compiling committee.c: too many arguments to function
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