On Tue, Nov 25, 2025 at 06:01:38PM +0000, Marc Zyngier wrote: > On Tue, 25 Nov 2025 17:01:23 +0000, > Anirudh Raybharam <[email protected]> wrote: > > > > From: Anirudh Rayabharam <[email protected]> > > > > From: Anirudh Rayabharam (Microsoft) <[email protected]> > > > > Currently SGIs are allocated only for the smp subsystem. The MSHV > > (Microsoft Hypervisor aka Hyper-V) code also needs an SGI that can be > > programmed into the SYNIC to receive intercepts from the hypervisor. The > > hypervisor would then assert this SGI whenever there is a guest > > VMEXIT. > > > > Allocate one SGI for MSHV use in addition to the SGIs allocated for > > IPIs. When running under MSHV, the full SGI range can be used i.e. no > > need to reserve SGIs 8-15 for the secure firmware. > > > > Since this SGI is needed only when running as a parent partition (i.e. > > we can create guest partitions), check for it before allocating an SGI. > > Sorry, but that's not an acceptable situation. > > SGIs are for Linux to use, nobody else, and that allocation must be
Why does this restriction exist? In the code SGIs 8-15 are left for secure firmware. So, things other than Linux can use SGIs. Why not MSHV then? > the same irrespective of whether Linux runs virtualised or not. This > also won't work with GICv5 (there are no SGIs at all), so this is > doomed from the very start, and would immediately create technical > debt. Hyper-V always presents a GICv3 so we don't need to worry about GICv5. > > If you want to signal an interrupt to Linux, expose a device with an > interrupt in a firmware table (i.e. not an SGI), and use that in your > driver. You mean in the ACPI tables? That would require us to modify the firmware to expose this virtual device right? Anirudh. > > Thanks, > > M. > > -- > Without deviation from the norm, progress is not possible.
