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?
CC Sven, Heiko for the entry.S changes.
