On Thu, 8 Feb 2024 07:21:40 +0000
"Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
> > From: Ankit Agrawal <ankita@xxxxxxxxxx>
> > Sent: Thursday, February 8, 2024 3:13 PM
> > >> > + * Determine how many bytes to be actually read from the
> > >> > device memory.
> > >> > + * Read request beyond the actual device memory size is
> > >> > filled with ~0,
> > >> > + * while those beyond the actual reported size is skipped.
> > >> > + */
> > >> > + if (offset >= memregion->memlength)
> > >> > + mem_count = 0;
> > >>
> > >> If mem_count == 0, going through nvgrace_gpu_map_and_read() is not
> > >> necessary.
> > >
> > > Harmless, other than the possibly unnecessary call through to
> > > nvgrace_gpu_map_device_mem(). Maybe both
> > nvgrace_gpu_map_and_read()
> > > and nvgrace_gpu_map_and_write() could conditionally return 0 as their
> > > first operation when !mem_count. Thanks,
> > >
> > >Alex
> >
> > IMO, this seems like adding too much code to reduce the call length for a
> > very specific case. If there aren't any strong opinion on this, I'm planning to
> > leave this code as it is.
>
> a slight difference. if mem_count==0 the result should always succeed
> no matter nvgrace_gpu_map_device_mem() succeeds or not. Of course
> if it fails it's already a big problem probably nobody cares about the subtle
> difference when reading non-exist range.
>
> but regarding to readability it's still clearer:
>
> if (mem_count)
> nvgrace_gpu_map_and_read();
>
The below has better flow imo vs conditionalizing the call to
map_and_read/write and subsequent error handling, but I don't think
either adds too much code. Thanks,
Alex
--- a/drivers/vfio/pci/nvgrace-gpu/main.c
+++ b/drivers/vfio/pci/nvgrace-gpu/main.c
@@ -429,6 +429,9 @@ nvgrace_gpu_map_and_read(struct nvgrace_gpu_vfio_pci_core_device *nvdev,
u64 offset = *ppos & VFIO_PCI_OFFSET_MASK;
int ret;
+ if (!mem_count)
+ return 0;
+
/*
* Handle read on the BAR regions. Map to the target device memory
* physical address and copy to the request read buffer.
@@ -547,6 +550,9 @@ nvgrace_gpu_map_and_write(struct nvgrace_gpu_vfio_pci_core_device *nvdev,
loff_t pos = *ppos & VFIO_PCI_OFFSET_MASK;
int ret;
+ if (!mem_count)
+ return 0;
+
ret = nvgrace_gpu_map_device_mem(index, nvdev);
if (ret)
return ret;
