On Tue, Jan 18, 2022 at 03:15:51PM +0100, Christian Borntraeger wrote: > Am 18.01.22 um 14:12 schrieb Mark Rutland: > > 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. > What exactly would the low-level interrupt handler need to do? Having looked around a bit, I think the best bet is to have irqentry_enter() check PF_VCPU in addition to PF_IDLE (which it checks via is_idle_task()), at which point nothing needs to change in the s390 entry code. I'm currently implementing that, let me have a go, and then we can see if that looks ok or whether we should do something else. > CC Sven, Heiko for the entry.S changes. I'll make sure you're all Cc'd when I send out vs with s390 patches. Thanks, Mark.
