[Qemu-devel] [PATCH v4 5/8] ahci: properly shadow the TFD register

[John Snow <jsnow@redhat.com>]

In a real AHCI device, several S/ATA registers are mirrored or shadowed
within the AHCI register set. These registers are not updated
synchronously for each read access, but are instead updated after a
Device-to-Host Register FIS packet is received. The D2H FIS contains
the values from these registers on the device.

In QEMU, by reaching directly into the device to grab these bits before
they are "sent," we may introduce race conditions where unexpected
values are present "before they are sent" which could cause issues for
some guests, particularly if an attempt is made to read the PxTFD
register prior to enabling the port, where incorrect values will be read.

This patch also addresses the boot-time values for the PxTFD and PxSIG
registers to bring them in line with the AHCI 1.3 specification.

Lastly, several fields (PxTFD, PxSIG and PxSACT) are read-only,
and any attempts to write to them should be ignored.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 hw/ide/ahci.c | 42 ++++++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 14 deletions(-)

diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index 932b0d5..5ff1442 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -78,8 +78,7 @@ static uint32_t  ahci_port_read(AHCIState *s, int port, int offset)
         val = pr->cmd;
         break;
     case PORT_TFDATA:
-        val = ((uint16_t)s->dev[port].port.ifs[0].error << 8) |
-              s->dev[port].port.ifs[0].status;
+        val = pr->tfdata;
         break;
     case PORT_SIG:
         val = pr->sig;
@@ -251,14 +250,13 @@ static void  ahci_port_write(AHCIState *s, int port, int offset, uint32_t val)
             check_cmd(s, port);
             break;
         case PORT_TFDATA:
-            s->dev[port].port.ifs[0].error = (val >> 8) & 0xff;
-            s->dev[port].port.ifs[0].status = val & 0xff;
+            /* Read Only. */
             break;
         case PORT_SIG:
-            pr->sig = val;
+            /* Read Only */
             break;
         case PORT_SCR_STAT:
-            pr->scr_stat = val;
+            /* Read Only */
             break;
         case PORT_SCR_CTL:
             if (((pr->scr_ctl & AHCI_SCR_SCTL_DET) == 1) &&
@@ -497,6 +495,8 @@ static void ahci_reset_port(AHCIState *s, int port)
     pr->scr_stat = 0;
     pr->scr_err = 0;
     pr->scr_act = 0;
+    pr->tfdata = 0x7F;
+    pr->sig = 0xFFFFFFFF;
     d->busy_slot = -1;
     d->init_d2h_sent = false;
 
@@ -528,16 +528,16 @@ static void ahci_reset_port(AHCIState *s, int port)
 
     s->dev[port].port_state = STATE_RUN;
     if (!ide_state->bs) {
-        s->dev[port].port_regs.sig = 0;
+        pr->sig = 0;
         ide_state->status = SEEK_STAT | WRERR_STAT;
     } else if (ide_state->drive_kind == IDE_CD) {
-        s->dev[port].port_regs.sig = SATA_SIGNATURE_CDROM;
+        pr->sig = SATA_SIGNATURE_CDROM;
         ide_state->lcyl = 0x14;
         ide_state->hcyl = 0xeb;
         DPRINTF(port, "set lcyl = %d\n", ide_state->lcyl);
         ide_state->status = SEEK_STAT | WRERR_STAT | READY_STAT;
     } else {
-        s->dev[port].port_regs.sig = SATA_SIGNATURE_DISK;
+        pr->sig = SATA_SIGNATURE_DISK;
         ide_state->status = SEEK_STAT | WRERR_STAT;
     }
 
@@ -563,7 +563,8 @@ static void debug_print_fis(uint8_t *fis, int cmd_len)
 
 static void ahci_write_fis_sdb(AHCIState *s, int port, uint32_t finished)
 {
-    AHCIPortRegs *pr = &s->dev[port].port_regs;
+    AHCIDevice *ad = &s->dev[port];
+    AHCIPortRegs *pr = &ad->port_regs;
     IDEState *ide_state;
     uint8_t *sdb_fis;
 
@@ -572,8 +573,8 @@ static void ahci_write_fis_sdb(AHCIState *s, int port, uint32_t finished)
         return;
     }
 
-    sdb_fis = &s->dev[port].res_fis[RES_FIS_SDBFIS];
-    ide_state = &s->dev[port].port.ifs[0];
+    sdb_fis = &ad->res_fis[RES_FIS_SDBFIS];
+    ide_state = &ad->port.ifs[0];
 
     /* clear memory */
     *(uint32_t*)sdb_fis = 0;
@@ -582,9 +583,14 @@ static void ahci_write_fis_sdb(AHCIState *s, int port, uint32_t finished)
     sdb_fis[0] = ide_state->error;
     sdb_fis[2] = ide_state->status & 0x77;
     s->dev[port].finished |= finished;
-    *(uint32_t*)(sdb_fis + 4) = cpu_to_le32(s->dev[port].finished);
+    *(uint32_t*)(sdb_fis + 4) = cpu_to_le32(ad->finished);
 
-    ahci_trigger_irq(s, &s->dev[port], PORT_IRQ_SDB_FIS);
+    /* Update shadow registers (except BSY 0x80 and DRQ 0x08) */
+    pr->tfdata = (ad->port.ifs[0].error << 8) |
+        (ad->port.ifs[0].status & 0x77) |
+        (pr->tfdata & 0x88);
+
+    ahci_trigger_irq(s, ad, PORT_IRQ_SDB_FIS);
 }
 
 static void ahci_write_fis_pio(AHCIDevice *ad, uint16_t len)
@@ -642,6 +648,10 @@ static void ahci_write_fis_pio(AHCIDevice *ad, uint16_t len)
     pio_fis[18] = 0;
     pio_fis[19] = 0;
 
+    /* Update shadow registers: */
+    pr->tfdata = (ad->port.ifs[0].error << 8) |
+        ad->port.ifs[0].status;
+
     if (pio_fis[2] & ERR_STAT) {
         ahci_trigger_irq(ad->hba, ad, PORT_IRQ_TF_ERR);
     }
@@ -693,6 +703,10 @@ static void ahci_write_fis_d2h(AHCIDevice *ad, uint8_t *cmd_fis)
         d2h_fis[i] = 0;
     }
 
+    /* Update shadow registers: */
+    pr->tfdata = (ad->port.ifs[0].error << 8) |
+        ad->port.ifs[0].status;
+
     if (d2h_fis[2] & ERR_STAT) {
         ahci_trigger_irq(ad->hba, ad, PORT_IRQ_TF_ERR);
     }
-- 
1.9.3