Re: [PATCH 2/2] IB/rdmavt: modify rdmavt/qp.c for UML

[Anton Ivanov]

On 04/01/2022 01:00, Randy Dunlap wrote:
> On 1/3/22 15:04, Jason Gunthorpe wrote:
> > On Sat, Jan 01, 2022 at 11:06:23PM -0800, Randy Dunlap wrote:
> > > When building rdmavt for ARCH=um, qp.c has a build error on a reference
> > > to the x86-specific cpuinfo field 'x86_cache_size'. This value is then
> > > used to determine whether to use cacheless_memcpy() or not.
> > > Provide a fake value to LLC for CONFIG_UML. Then provide a separate
> > > verison of cacheless_memcpy() for CONFIG_UML that is just a plain
> > > memcpy(), like the calling code uses.
> > >
> > > Prevents these build errors:
> > >
> > > ../drivers/infiniband/sw/rdmavt/qp.c: In function ‘rvt_wss_llc_size’:
> > > ../drivers/infiniband/sw/rdmavt/qp.c:88:23: error: ‘struct cpuinfo_um’ has no member named ‘x86_cache_size’; did you mean ‘x86_capability’?
> > >    return boot_cpu_data.x86_cache_size;
> > >
> > > ../drivers/infiniband/sw/rdmavt/qp.c: In function ‘cacheless_memcpy’:
> > > ../drivers/infiniband/sw/rdmavt/qp.c:100:2: error: implicit declaration of function ‘__copy_user_nocache’; did you mean ‘copy_user_page’? [-Werror=implicit-function-declaration]
> > >    __copy_user_nocache(dst, (void __user *)src, n, 0);
> > >
> > > Fixes: 68f5d3f3b654 ("um: add PCI over virtio emulation driver")
> > > Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> > >   drivers/infiniband/sw/rdmavt/qp.c |   12 ++++++++++++
> > >   1 file changed, 12 insertions(+)
> > >
> > > +++ linux-next-20211224/drivers/infiniband/sw/rdmavt/qp.c
> > > @@ -84,10 +84,15 @@ EXPORT_SYMBOL(ib_rvt_state_ops);
> > >   /* platform specific: return the last level cache (llc) size, in KiB */
> > >   static int rvt_wss_llc_size(void)
> > >   {
> > > +#if !defined(CONFIG_UML)
> > >   	/* assume that the boot CPU value is universal for all CPUs */
> > >   	return boot_cpu_data.x86_cache_size;
> > > +#else /* CONFIG_UML */
> > > +	return 1024;	/* fake 1 MB LLC size */
> > > +#endif
> > >   }
> > >   
> > > +#if !defined(CONFIG_UML)
> > >   /* platform specific: cacheless copy */
> > >   static void cacheless_memcpy(void *dst, void *src, size_t n)
> > >   {
> > > @@ -99,6 +104,13 @@ static void cacheless_memcpy(void *dst,
> > >   	 */
> > >   	__copy_user_nocache(dst, (void __user *)src, n, 0);
> > >   }
> > > +#else
> > > +/* for CONFIG_UML, this is just a plain memcpy() */
> > > +static void cacheless_memcpy(void *dst, void *src, size_t n)
> > > +{
> > > +	memcpy(dst, src, n);
> > > +}
> > > +#endif
> >
> > memcpy is not the same thing as __copy_user - the hint is in the
> > __user cast..
> >
> > It should by copy_from_user(), I think, and this is all just somehow
> > broken to not check the return code.
>
> Thanks.
>
> > Why are you trying to make a HW driver compile on UML? Is there any
> > way to even use a driver like this in a UML environment?
>
> I'm just trying to clean up lots of UML build errors.
> I'm quite happy just making the driver depend on !UML.
>
> UML maintainers, what do you think?
>
> Thanks again.

I would suggest that we just !UML this driver.

--
Anton R. Ivanov
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