[Qemu-devel] [PATCH 2/2] AHCI: Protect cmd register

[John Snow <jsnow@redhat.com>]

Many bits in the CMD register are supposed to be strictly read-only.
We should not be deleting them on every write.

As a side-effect: pay explicit attention to when a guest marks off
the FIS Receive or Start bits, and disable the status bits ourselves,
instead of letting them implicitly fall off.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 hw/ide/ahci.c | 26 +++++++++++++++++++++++++-
 hw/ide/ahci.h |  2 ++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index 42bbf7f..b386a25 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -52,7 +52,9 @@ static void ahci_init_d2h(AHCIDevice *ad);
 static int ahci_dma_prepare_buf(IDEDMA *dma, int is_write);
 static void ahci_commit_buf(IDEDMA *dma, uint32_t tx_bytes);
 static void ahci_map_clb_address(AHCIDevice *ad);
+static void ahci_unmap_clb_address(AHCIDevice *ad);
 static void ahci_map_fis_address(AHCIDevice *ad);
+static void ahci_unmap_fis_address(AHCIDevice *ad);
 
 
 static uint32_t  ahci_port_read(AHCIState *s, int port, int offset)
@@ -223,16 +225,24 @@ static void  ahci_port_write(AHCIState *s, int port, int offset, uint32_t val)
             ahci_check_irq(s);
             break;
         case PORT_CMD:
-            pr->cmd = val & ~(PORT_CMD_LIST_ON | PORT_CMD_FIS_ON);
+            /* Block any Read-only fields from being set;
+             * including LIST_ON and FIS_ON. */
+            pr->cmd = (pr->cmd & PORT_CMD_RO_MASK) | (val & ~PORT_CMD_RO_MASK);
 
             if (pr->cmd & PORT_CMD_START) {
                 pr->cmd |= PORT_CMD_LIST_ON;
                 ahci_map_clb_address(&s->dev[port]);
+            } else if (pr->cmd & PORT_CMD_LIST_ON) {
+                ahci_unmap_clb_address(&s->dev[port]);
+                pr->cmd = pr->cmd & ~(PORT_CMD_LIST_ON);
             }
 
             if (pr->cmd & PORT_CMD_FIS_RX) {
                 pr->cmd |= PORT_CMD_FIS_ON;
                 ahci_map_fis_address(&s->dev[port]);
+            } else if (pr->cmd & PORT_CMD_FIS_ON) {
+                ahci_unmap_fis_address(&s->dev[port]);
+                pr->cmd = pr->cmd & ~(PORT_CMD_FIS_ON);
             }
 
             /* XXX usually the FIS would be pending on the bus here and
@@ -566,6 +576,13 @@ static void ahci_map_fis_address(AHCIDevice *ad)
              ((uint64_t)pr->fis_addr_hi << 32) | pr->fis_addr, 256);
 }
 
+static void ahci_unmap_fis_address(AHCIDevice *ad)
+{
+    dma_memory_unmap(ad->hba->as, ad->res_fis, 256,
+                     DMA_DIRECTION_FROM_DEVICE, 256);
+    ad->res_fis = NULL;
+}
+
 static void ahci_map_clb_address(AHCIDevice *ad)
 {
     AHCIPortRegs *pr = &ad->port_regs;
@@ -574,6 +591,13 @@ static void ahci_map_clb_address(AHCIDevice *ad)
              ((uint64_t)pr->lst_addr_hi << 32) | pr->lst_addr, 1024);
 }
 
+static void ahci_unmap_clb_address(AHCIDevice *ad)
+{
+    dma_memory_unmap(ad->hba->as, ad->lst, 1024,
+                     DMA_DIRECTION_FROM_DEVICE, 1024);
+    ad->lst = NULL;
+}
+
 static void ahci_write_fis_sdb(AHCIState *s, int port, uint32_t finished)
 {
     AHCIDevice *ad = &s->dev[port];
diff --git a/hw/ide/ahci.h b/hw/ide/ahci.h
index 99aa0c9..501c002 100644
--- a/hw/ide/ahci.h
+++ b/hw/ide/ahci.h
@@ -132,6 +132,8 @@
 #define PORT_CMD_ICC_PARTIAL      (0x2 << 28) /* Put i/f in partial state */
 #define PORT_CMD_ICC_SLUMBER      (0x6 << 28) /* Put i/f in slumber state */
 
+#define PORT_CMD_RO_MASK          0x007dffe0 /* Which CMD bits are read only? */
+
 /* ap->flags bits */
 #define AHCI_FLAG_NO_NCQ                  (1 << 24)
 #define AHCI_FLAG_IGN_IRQ_IF_ERR          (1 << 25) /* ignore IRQ_IF_ERR */
-- 
1.9.3