On Tue, Jun 21, 2022 at 11:53:06AM -0400, Alexander Bulekov wrote:
> On 220621 1630, Peter Maydell wrote:
> > On Thu, 9 Jun 2022 at 14:59, Alexander Bulekov <alx...@bu.edu> wrote:
> > > diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
> > > index 44dacfa224..ab1ad0f7a8 100644
> > > --- a/include/hw/pci/pci.h
> > > +++ b/include/hw/pci/pci.h
> > > @@ -834,8 +834,17 @@ static inline MemTxResult pci_dma_rw(PCIDevice *dev,
> > > dma_addr_t addr,
> > > void *buf, dma_addr_t len,
> > > DMADirection dir, MemTxAttrs attrs)
> > > {
> > > - return dma_memory_rw(pci_get_address_space(dev), addr, buf, len,
> > > - dir, attrs);
> > > + bool prior_engaged_state;
> > > + MemTxResult result;
> > > +
> > > + prior_engaged_state = dev->qdev.engaged_in_io;
> > > +
> > > + dev->qdev.engaged_in_io = true;
> > > + result = dma_memory_rw(pci_get_address_space(dev), addr, buf, len,
> > > + dir, attrs);
> > > + dev->qdev.engaged_in_io = prior_engaged_state;
> > > +
> > > + return result;
> >
> > Why do we need to do something in this pci-specific function ?
> > I was expecting this to only need changes at the generic-to-all-devices
> > level.
>
> Both of these handle the BH->DMA->MMIO case. Unlike MMIO, I don't think
> there is any neat way to set the engaged_in_io flag as we enter a BH. So
> instead, we try to set it when a device initiates DMA.
>
> The pci function lets us do that since we get a glimpse of the dev/qdev
> (unlike the dma_memory_... functions).
...
> > > @@ -302,6 +310,10 @@ static MemTxResult dma_buf_rw(void *buf, dma_addr_t
> > > len, dma_addr_t *residual,
> > > xresidual -= xfer;
> > > }
> > >
> > > + if (dev) {
> > > + dev->engaged_in_io = prior_engaged_state;
> > > + }
> >
> > Not all DMA goes through dma_buf_rw() -- why does it need changes?
>
> This one has the same goal, but accesses the qdev through sg, instead of
> PCI.
Should dma_*() APIs take a reentrancy guard argument so that all DMA
accesses are systematically covered?
/* Define this in the memory API */
typedef struct {
bool engaged_in_io;
} MemReentrancyGuard;
/* Embed MemReentrancyGuard in DeviceState */
...
/* Require it in dma_*() APIs */
static inline MemTxResult dma_memory_rw(AddressSpace *as, dma_addr_t addr,
void *buf, dma_addr_t len,
DMADirection dir, MemTxAttrs attrs,
MemReentrancyGuard *guard);
/* Call dma_*() APIs like this... */
static inline MemTxResult pci_dma_rw(PCIDevice *dev, dma_addr_t addr,
void *buf, dma_addr_t len,
DMADirection dir, MemTxAttrs attrs)
{
return dma_memory_rw(pci_get_address_space(dev), addr, buf, len,
dir, attrs, &dev->qdev.reentrancy_guard);
}
Stefan
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