ide: remove hardcoded 2GiB transactional limit

Not that you can request a >2GiB transaction, but that's why checking
for it makes no sense anymore.

With the newer 'limit' parameter to prepare_buf, we no longer need a
static limit. The maximum limit is still 2GiB, but the limit parameter
is set to the current transaction size, which cannot surpass 32MiB
(512 * 65536). If the PRDT surpasses the transactional size, then,
we'll just carry out the normative underflow handling pathways instead
of needing an extra, strange pathway that worries about hitting some
logistical cap for the largest sglist we can support -- we'll never
even attempt to build one that big anymore.

Reported-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1445902682-20051-1-git-send-email-jsnow@redhat.com

diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index 21f76ed86e4370f3b75d3814f707c18e9d91f133..f547ebb46cd358f22a1b0f3a688c1e9ad63e0e4a 100644 (file)
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -804,8 +804,21 @@ static int prdt_tbl_entry_size(const AHCI_SG *tbl)
     return (le32_to_cpu(tbl->flags_size) & AHCI_PRDT_SIZE_MASK) + 1;
 }
 
+/**
+ * Fetch entries in a guest-provided PRDT and convert it into a QEMU SGlist.
+ * @ad: The AHCIDevice for whom we are building the SGList.
+ * @sglist: The SGList target to add PRD entries to.
+ * @cmd: The AHCI Command Header that describes where the PRDT is.
+ * @limit: The remaining size of the S/ATA transaction, in bytes.
+ * @offset: The number of bytes already transferred, in bytes.
+ *
+ * The AHCI PRDT can describe up to 256GiB. S/ATA only support transactions of
+ * up to 32MiB as of ATA8-ACS3 rev 1b, assuming a 512 byte sector size. We stop
+ * building the sglist from the PRDT as soon as we hit @limit bytes,
+ * which is <= INT32_MAX/2GiB.
+ */
 static int ahci_populate_sglist(AHCIDevice *ad, QEMUSGList *sglist,
-                                AHCICmdHdr *cmd, int64_t limit, int32_t offset)
+                                AHCICmdHdr *cmd, int64_t limit, uint64_t offset)
 {
     uint16_t opts = le16_to_cpu(cmd->opts);
     uint16_t prdtl = le16_to_cpu(cmd->prdtl);
@@ -823,14 +836,6 @@ static int ahci_populate_sglist(AHCIDevice *ad, QEMUSGList *sglist,
     IDEBus *bus = &ad->port;
     BusState *qbus = BUS(bus);
 
-    /*
-     * Note: AHCI PRDT can describe up to 256GiB. SATA/ATA only support
-     * transactions of up to 32MiB as of ATA8-ACS3 rev 1b, assuming a
-     * 512 byte sector size. We limit the PRDT in this implementation to
-     * a reasonably large 2GiB, which can accommodate the maximum transfer
-     * request for sector sizes up to 32K.
-     */
-
     if (!prdtl) {
         DPRINTF(ad->port_no, "no sg list given by guest: 0x%08x\n", opts);
         return -1;
@@ -880,13 +885,6 @@ static int ahci_populate_sglist(AHCIDevice *ad, QEMUSGList *sglist,
             qemu_sglist_add(sglist, le64_to_cpu(tbl[i].addr),
                             MIN(prdt_tbl_entry_size(&tbl[i]),
                                 limit - sglist->size));
-            if (sglist->size > INT32_MAX) {
-                error_report("AHCI Physical Region Descriptor Table describes "
-                             "more than 2 GiB.");
-                qemu_sglist_destroy(sglist);
-                r = -1;
-                goto out;
-            }
         }
     }
 

diff --git a/hw/ide/internal.h b/hw/ide/internal.h
index 05e93ffe3bcde446deee176ea55b3ea6980ef9ff..e4629b023ad7449612f8544e1d80365c33ce78a2 100644 (file)
--- a/hw/ide/internal.h
+++ b/hw/ide/internal.h
@@ -397,7 +397,7 @@ struct IDEState {
     struct iovec iov;
     QEMUIOVector qiov;
     /* ATA DMA state */
-    int32_t io_buffer_offset;
+    uint64_t io_buffer_offset;
     int32_t io_buffer_size;
     QEMUSGList sg;
     /* PIO transfer handling */

diff --git a/hw/ide/pci.c b/hw/ide/pci.c
index d31ff885b7a4f4946a1606b529596d52a94c7742..9c54b378d669b24b837fea4887a2ec38f05dd2cb 100644 (file)
--- a/hw/ide/pci.c
+++ b/hw/ide/pci.c
@@ -103,13 +103,6 @@ static int32_t bmdma_prepare_buf(IDEDMA *dma, int32_t limit)
                 qemu_sglist_add(&s->sg, bm->cur_prd_addr, sg_len);
             }
 
-            /* Note: We limit the max transfer to be 2GiB.
-             * This should accommodate the largest ATA transaction
-             * for LBA48 (65,536 sectors) and 32K sector sizes. */
-            if (s->sg.size > INT32_MAX) {
-                error_report("IDE: sglist describes more than 2GiB.");
-                break;
-            }
             bm->cur_prd_addr += l;
             bm->cur_prd_len -= l;
             s->io_buffer_size += l;