Re: [PATCH 1/4] drivers: hv: dxgkrnl: core code

Greg KH
2020-08-28T06:15:09Z

On Thu, Aug 27, 2020 at 04:45:55PM -0700, Iouri Tarassov wrote:
>
> On 8/14/2020 5:57 AM, Greg KH wrote:
> > On Fri, Aug 14, 2020 at 08:38:53AM -0400, Sasha Levin wrote:
> > > Add support for a Hyper-V based vGPU implementation that exposes the
> > > DirectX API to Linux userspace.
> >
> > Api questions:
> >
> > > +struct d3dkmthandle {
> > > + union {
> > > + struct {
> > > + u32 instance : 6;
> > > + u32 index : 24;
> > > + u32 unique : 2;
> >
> > What is the endian of this?
> >
> > > + };
> > > + u32 v;
> > > + };
> > > +};
> > > +
> > > +extern const struct d3dkmthandle zerohandle;
> > > +
> The definition is the same as on the Windows side. The driver communicates
> with a Windows host, so I do not expect any issues with endiannes. Windows
> currently runs only on the little endian platforms.

As I mentioned before, you need to document that somewhere (like maybe
preventing your code from being built on big endian systems?)

> User mode applications see this as an opaque 32 bit value (D3DKMTHANDLE). I
> prefer not to use the u32 definition to avoid mistakes when another integer
> or a 64-bit handle is assigned to the handle or  the handle is assigned to a
> 64 or 32 bit integer variable. There are many handles in the driver model
> (shared NT handle, d3dkmthandle, etc). Using a specific type allows to avoid
> assigning one handle to another.

Specific types are great, that is fine.

> > > +struct ntstatus {
> > > + union {
> > > + struct {
> > > + int code : 16;
> > > + int facility : 13;
> > > + int customer : 1;
> > > + int severity : 2;
> >
> > Same here.
> >
> > Are these things that cross the user/kernel boundry?
> >
> > And why int on one and u32 on the other?
> >
> > > + };
> > > + int v;
> > > + };
> > > +};
> > > +
> "struct ntstatus" follows the definition for NTSTATUS on the Windows side.
> NTSTATUS is an integer where the negative values indicate errors. It is
> success otherwise. NTSTATUS is returned by the VM bus messages from host.
> IOCTLs from the driver return Linux negative error code or NTSTATUS positive
> success codes. DxCore applications expect certain positive success codes.
> DxCore is a shared library, which translates the D3DKMT* Windows interface
> to Linux ioctls. Applications link with DxCore to use a paravirtualized GPU.
> D3DKMTHANDLE is a 32-bit unsigned value (bitfield), not an integer.

Ok, again, please document this, and as these fields are crossing the
kernel/user boundry, use the correct types (hint, 'int' is never that
type).

> > > +struct winluid {
> > > + uint a;
> > > + uint b;
> >
> > And now uint? Come on, be consistent please :)
> Sorry about this. This came from the Windows size where we use UINT a lot.
> All uints will be replaced by u32 in the next patch set.

thank you.

greg k-h