[ipxe-devel] [PATCH 0/2] mask lack of KVM's FXSAVE/FXRSTOR emulation in the QEMU build

Gerd Hoffmann kraxel at redhat.com
Thu Oct 27 15:04:29 UTC 2016

On Do, 2016-10-27 at 00:13 +0200, Laszlo Ersek wrote:
> iPXE commit 71560d185475 added FXSAVE and FXRSTOR instructions. On KVM
> hosts without "unrestricted_guest" support, these expose a gap in KVM's
> big real mode emulation, leading to guest crashes.
> Radim has just posted the KVM patches. I think it might make sense to
> suppress the regression of user experience within iPXE, until the KVM
> feature reaches end-users. (Especially because the workaround for the
> Tivoli VMM bug, which needed the FXSAVE and FXRSTOR instructions, is not
> useful on KVM.)

Making the Tivoli VMM bug workaround configurable seems to be useful
outside qemu scope too, see the reports on fxsave issues on physical

Patches look good to me.

Note that a new qemu version is just around the corner.  Having this
issue fixed in quickly would be great, we can pick it up by simply
rebasing to a fixed version then.  But that'll work out only in case the
fixed land in ipxe master before qemu freeze, which is November 1st.


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