From: Guenter Roeck <li...@roeck-us.net> 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 <li...@roeck-us.net> --- hw/scsi/esp-pci.c | 4 ++-- hw/scsi/esp.c | 33 ++++++++++++++++++++++++++------- hw/scsi/trace-events | 1 + include/hw/scsi/esp.h | 2 ++ 4 files changed, 31 insertions(+), 9 deletions(-) diff --git a/hw/scsi/esp-pci.c b/hw/scsi/esp-pci.c index d956909186..6b0bbb9b7f 100644 --- a/hw/scsi/esp-pci.c +++ b/hw/scsi/esp-pci.c @@ -313,8 +313,8 @@ static void esp_pci_hard_reset(DeviceState *dev) static const VMStateDescription vmstate_esp_pci_scsi = { .name = "pciespscsi", - .version_id = 0, - .minimum_version_id = 0, + .version_id = 1, + .minimum_version_id = 1, .fields = (VMStateField[]) { VMSTATE_PCI_DEVICE(parent_obj, PCIESPState), VMSTATE_BUFFER_UNSAFE(dma_regs, PCIESPState, 0, 8 * sizeof(uint32_t)), diff --git a/hw/scsi/esp.c b/hw/scsi/esp.c index 630d923623..ca8b36c0c5 100644 --- a/hw/scsi/esp.c +++ b/hw/scsi/esp.c @@ -286,11 +286,8 @@ static void esp_do_dma(ESPState *s) esp_dma_done(s); } -void esp_command_complete(SCSIRequest *req, uint32_t status, - size_t resid) +static void esp_report_command_complete(ESPState *s, uint32_t status) { - ESPState *s = req->hba_private; - trace_esp_command_complete(); if (s->ti_size != 0) { trace_esp_command_complete_unexpected(); @@ -311,6 +308,23 @@ void esp_command_complete(SCSIRequest *req, uint32_t status, } } +void esp_command_complete(SCSIRequest *req, uint32_t status, + size_t resid) +{ + ESPState *s = req->hba_private; + + if (s->rregs[ESP_RSTAT] & STAT_INT) { + /* Defer handling command complete until the previous + * interrupt has been handled. + */ + trace_esp_command_complete_deferred(); + s->deferred_status = status; + s->deferred_complete = true; + return; + } + esp_report_command_complete(s, status); +} + void esp_transfer_data(SCSIRequest *req, uint32_t len) { ESPState *s = req->hba_private; @@ -422,7 +436,10 @@ uint64_t esp_reg_read(ESPState *s, uint32_t saddr) s->rregs[ESP_RSTAT] &= ~STAT_TC; s->rregs[ESP_RSEQ] = SEQ_CD; esp_lower_irq(s); - + if (s->deferred_complete) { + esp_report_command_complete(s, s->deferred_status); + s->deferred_complete = false; + } return old_val; case ESP_TCHI: /* Return the unique id if the value has never been written */ @@ -582,6 +599,8 @@ const VMStateDescription vmstate_esp = { VMSTATE_UINT32(ti_wptr, ESPState), VMSTATE_BUFFER(ti_buf, ESPState), VMSTATE_UINT32(status, ESPState), + VMSTATE_UINT32(deferred_status, ESPState), + VMSTATE_BOOL(deferred_complete, ESPState), VMSTATE_UINT32(dma, ESPState), VMSTATE_PARTIAL_BUFFER(cmdbuf, ESPState, 16), VMSTATE_BUFFER_START_MIDDLE_V(cmdbuf, ESPState, 16, 4), @@ -671,8 +690,8 @@ static void sysbus_esp_hard_reset(DeviceState *dev) static const VMStateDescription vmstate_sysbus_esp_scsi = { .name = "sysbusespscsi", - .version_id = 0, - .minimum_version_id = 0, + .version_id = 1, + .minimum_version_id = 1, .fields = (VMStateField[]) { VMSTATE_STRUCT(esp, SysBusESPState, 0, vmstate_esp, ESPState), VMSTATE_END_OF_LIST() diff --git a/hw/scsi/trace-events b/hw/scsi/trace-events index 0fb6a99616..2fe8a7c062 100644 --- a/hw/scsi/trace-events +++ b/hw/scsi/trace-events @@ -167,6 +167,7 @@ esp_handle_satn_stop(uint32_t cmdlen) "cmdlen %d" esp_write_response(uint32_t status) "Transfer status (status=%d)" esp_do_dma(uint32_t cmdlen, uint32_t len) "command len %d + %d" esp_command_complete(void) "SCSI Command complete" +esp_command_complete_deferred(void) "SCSI Command complete deferred" esp_command_complete_unexpected(void) "SCSI command completed unexpectedly" esp_command_complete_fail(void) "Command failed" esp_transfer_data(uint32_t dma_left, int32_t ti_size) "transfer %d/%d" diff --git a/include/hw/scsi/esp.h b/include/hw/scsi/esp.h index 682a0d2de0..adab63d1c9 100644 --- a/include/hw/scsi/esp.h +++ b/include/hw/scsi/esp.h @@ -23,6 +23,8 @@ struct ESPState { int32_t ti_size; uint32_t ti_rptr, ti_wptr; uint32_t status; + uint32_t deferred_status; + bool deferred_complete; uint32_t dma; uint8_t ti_buf[TI_BUFSZ]; SCSIBus bus; -- 2.20.1