@@ -849,6 +849,7 @@ static void ide_dma_cb(void *opaque, int ret)
int64_t sector_num;
uint64_t offset;
bool stay_active = false;
+ int32_t prep_size = 0;
if (ret == -EINVAL) {
ide_dma_error(s);
@@ -863,13 +864,15 @@ static void ide_dma_cb(void *opaque, int ret)
}
}
- n = s->io_buffer_size >> 9;
- if (n > s->nsector) {
- /* The PRDs were longer than needed for this request. Shorten them so
- * we don't get a negative remainder. The Active bit must remain set
- * after the request completes. */
+ if (s->io_buffer_size > s->nsector * 512) {
+ /*
+ * The PRDs were longer than needed for this request.
+ * The Active bit must remain set after the request completes.
+ */
n = s->nsector;
stay_active = true;
+ } else {
+ n = s->io_buffer_size >> 9;
}
sector_num = ide_get_sector(s);
@@ -892,9 +895,20 @@ static void ide_dma_cb(void *opaque, int ret)
n = s->nsector;
s->io_buffer_index = 0;
s->io_buffer_size = n * 512;
- if (s->bus->dma->ops->prepare_buf(s->bus->dma, s->io_buffer_size) < 512) {
- /* The PRDs were too short. Reset the Active bit, but don't raise an
- * interrupt. */
+ prep_size = s->bus->dma->ops->prepare_buf(s->bus->dma, s->io_buffer_size);
+ /* prepare_buf() must succeed and respect the limit */
+ assert(prep_size >= 0 && prep_size <= n * 512);
+
+ /*
+ * Now prep_size stores the number of bytes in the sglist, and
+ * s->io_buffer_size stores the number of bytes described by the PRDs.
+ */
+
+ if (prep_size < n * 512) {
+ /*
+ * The PRDs are too short for this request. Error condition!
+ * Reset the Active bit and don't raise the interrupt.
+ */
s->status = READY_STAT | SEEK_STAT;
dma_buf_commit(s, 0);
goto eot;
The commit a718978ed58a from July 2015 introduced the assertion which implies that the size of successful DMA transfers handled in ide_dma_cb() should be multiple of 512 (the size of a sector). But guest systems can initiate DMA transfers that don't fit this requirement. For fixing that let's check the number of bytes prepared for the transfer by the prepare_buf() handler. The code in ide_dma_cb() must behave according to the Programming Interface for Bus Master IDE Controller (Revision 1.0 5/16/94): 1. If PRDs specified a smaller size than the IDE transfer size, then the Interrupt and Active bits in the Controller status register are not set (Error Condition). 2. If the size of the physical memory regions was equal to the IDE device transfer size, the Interrupt bit in the Controller status register is set to 1, Active bit is set to 0. 3. If PRDs specified a larger size than the IDE transfer size, the Interrupt and Active bits in the Controller status register are both set to 1. Signed-off-by: Alexander Popov <alex.popov@linux.com> --- hw/ide/core.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-)