[Xen-devel] Status of FLR in Xen 4.4

[Matthias <matthias.kannenberg@xxxxxxxxxxxxxx>]

Hi everyone,

I would like to ask what the current status of FLR, or better of FLR emulation is in latest Xen and if we can expect better support in the future.

I'm asking because with xl (latest build and traditional qemu, not upstream), I always had problems with rebooting domUs which have vga cards passed through to them, because appearently they don't get reinitialized and then cause either bluescreens (windows), blackscreens (linux) or the complete freeze of the dom0. As far as I understood this is caused by the vga card do not have FLR capability (lspci -vvv shows FLReset-). So while lately rebooting sometimes works on windows, it never works on linux domUs and it appears that xl is simply not really capable of dealing with reboots with non-FLR'ed vga cards passed through the domUs and I have to reboot the dom0 to get the vga cards running again.

Is this the current status or is this supposed to work and I only have a problem on my setup?

Also, I'm specifically referring to xl because back in the day when I used xm with xen 4.0 and 4.1, this never was an issue and i could reboot both linux and windows domUs without issues as often as I wanted (with the same hardware setup I now use with xl). So to me it seems that there is a possibility to handle non-FLR'ed vga cards gracefully, but xl simply isn't capable of that / does not do that.

It would be great to have a quick roundup of the current situation and future plans, because I'm planing a project to use xen's vga passthrough in a cloud / big data setup and the unreliable reboot behaviour is currently a deal breaker for me.

Thanks in advance!

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