Hi Mark, Mark Rutland <mark.rutland@xxxxxxx> writes: > On Tue, Jan 18, 2022 at 01:42:26PM +0100, Christian Borntraeger wrote: >> >> >> Am 18.01.22 um 13:02 schrieb Mark Rutland: >> > On Mon, Jan 17, 2022 at 06:45:36PM +0100, Paolo Bonzini wrote: >> > > On 1/14/22 16:19, Mark Rutland wrote: >> > > > I also think there is another issue here. When an IRQ is taken from SIE, will >> > > > user_mode(regs) always be false, or could it be true if the guest userspace is >> > > > running? If it can be true I think tha context tracking checks can complain, >> > > > and it*might* be possible to trigger a panic(). >> > > >> > > I think that it would be false, because the guest PSW is in the SIE block >> > > and switched on SIE entry and exit, but I might be incorrect. >> > >> > Ah; that's the crux of my confusion: I had thought the guest PSW would >> > be placed in the regular lowcore *_old_psw slots. From looking at the >> > entry asm it looks like the host PSW (around the invocation of SIE) is >> > stored there, since that's what the OUTSIDE + SIEEXIT handling is >> > checking for. >> > >> > Assuming that's correct, I agree this problem doesn't exist, and there's >> > only the common RCU/tracing/lockdep management to fix. >> >> Will you provide an s390 patch in your next iteration or shall we then do >> one as soon as there is a v2? We also need to look into vsie.c where we >> also call sie64a > > I'm having a go at that now; my plan is to try to have an s390 patch as > part of v2 in the next day or so. > > Now that I have a rough idea of how SIE and exception handling works on > s390, I think the structural changes to kvm-s390.c:__vcpu_run() and > vsie.c:do_vsie_run() are fairly simple. > > The only open bit is exactly how/where to identify when the interrupt > entry code needs to wake RCU. I can add a per-cpu variable or thread > flag to indicate that we're inside that EQS, or or I could move the irq > enable/disable into the sie64a asm and identify that as with the OUTSIDE > macro in the entry asm. I wonder whether the code in irqentry_enter() should call a function is_eqs() instead of is_idle_task(). The default implementation would be just a #ifndef is_eqs #define is_eqs is_idle_task #endif and if an architecture has special requirements, it could just define is_eqs() and do the required checks there. This way the architecture could define whether it's a percpu bit, a cpu flag or something else. /Sven
