diff options
| author | Guenter Roeck <linux@roeck-us.net> | 2018-11-29 09:17:42 -0800 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2019-01-11 13:57:24 +0100 |
| commit | ea84a44250f79566484692bb000e97776ac66047 (patch) | |
| tree | 438608bd3b63f32142e711889f730de90b5ac9b9 /ioport.c | |
| parent | c2d6eeda016887f5d11401cd20281a356e226b51 (diff) | |
scsi: esp: Defer command completion until previous interrupts have been handled
The guest OS reads RSTAT, RSEQ, and RINTR, and expects those registers
to reflect a consistent state. However, it is possible that the registers
can change after RSTAT was read, but before RINTR is read, when
esp_command_complete() is called.
Guest OS qemu
-------- ----
[handle interrupt]
Read RSTAT
esp_command_complete()
RSTAT = STAT_ST
esp_dma_done()
RSTAT |= STAT_TC
RSEQ = 0
RINTR = INTR_BS
Read RSEQ
Read RINTR RINTR = 0
RSTAT &= ~STAT_TC
RSEQ = SEQ_CD
The guest OS would then try to handle INTR_BS combined with an old
value of RSTAT. This sometimes resulted in lost events, spurious
interrupts, guest OS confusion, and stalled SCSI operations.
A typical guest error log (observed with various versions of Linux)
looks as follows.
scsi host1: Spurious irq, sreg=13.
...
scsi host1: Aborting command [84531f10:2a]
scsi host1: Current command [f882eea8:35]
scsi host1: Queued command [84531f10:2a]
scsi host1: Active command [f882eea8:35]
scsi host1: Dumping command log
scsi host1: ent[15] CMD val[44] sreg[90] seqreg[00] sreg2[00] ireg[20] ss[00] event[0c]
scsi host1: ent[16] CMD val[01] sreg[90] seqreg[00] sreg2[00] ireg[20] ss[02] event[0c]
scsi host1: ent[17] CMD val[43] sreg[90] seqreg[00] sreg2[00] ireg[20] ss[02] event[0c]
scsi host1: ent[18] EVENT val[0d] sreg[92] seqreg[04] sreg2[00] ireg[18] ss[00] event[0c]
...
Defer handling command completion until previous interrupts have been
handled to fix the problem.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Diffstat (limited to 'ioport.c')
0 files changed, 0 insertions, 0 deletions