On Thu, Jul 25, 2024 at 10:29:18PM +0100, David Woodhouse wrote: > > > > Then can't we fix it by interrupting all CPUs right after LM? > > > > > > > > To me that seems like a cleaner approach - we then compartmentalize > > > > the ABI issue - kernel has its own ABI against userspace, > > > > devices have their own ABI against kernel. > > > > It'd mean we need a way to detect that interrupt was sent, > > > > maybe yet another counter inside that structure. > > > > > > > > WDYT? > > > > > > > > By the way the same idea would work for snapshots - > > > > some people wanted to expose that info to userspace, too. > > Those people included me. I wanted to interrupt all the vCPUs, even the > ones which were in userspace at the moment of migration, and have the > kernel deal with passing it on to userspace via a different ABI. > > It ends up being complex and intricate, and requiring a lot of new > kernel and userspace support. I gave up on it in the end for snapshots, > and didn't go there again for this.
Maybe become you insist on using ACPI? I see a fairly simple way to do it. For example, with virtio: one vq per CPU, with a single outstanding buffer, callback copies from the buffer into the userspace visible memory. Want me to show you the code? -- MST
