Re: [Xen-devel] [PATCH v3] xen: make sure stop_machine_run() is always called in a tasklet

[Jürgen Groß <jgross@xxxxxxxx>]

On 02.03.20 10:06, Jan Beulich wrote:
> On 29.02.2020 06:47, Jürgen Groß wrote:
> > On 28.02.20 20:06, Andrew Cooper wrote:
> > > On 28/02/2020 17:13, Juergen Gross wrote:
> > > > @@ -700,6 +688,32 @@ int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) 
> > > > buf, unsigned long len)
> > > >        return ret;
> > > >    }
> > > >    
> > > > +int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void) buf, unsigned long len)
> > > > +{
> > > > +    int ret;
> > > > +    struct ucode_buf *buffer;
> > > > +
> > > > +    if ( len != (uint32_t)len )
> > > > +        return -E2BIG;
> > > > +
> > > > +    if ( microcode_ops == NULL )
> > > > +        return -EINVAL;
> > > > +
> > > > +    buffer = xmalloc_flex_struct(struct ucode_buf, buffer, len);
> > > > +    if ( !buffer )
> > > > +        return -ENOMEM;
> > > > +
> > > > +    ret = copy_from_guest(buffer->buffer, buf, len);
> > > > +    if ( ret )
> > > > +    {
> > > > +        xfree(buffer);
> > > > +        return -EFAULT;
> > > > +    }
> > > > +    buffer->len = len;
> > > > +
> > > > +    return continue_hypercall_on_cpu(0, microcode_update_helper, buffer);
> > > Any reason why cpu 0 here?  There is no restriction at the moment, and
> > > running the tasklet on the current CPU is surely better than poking
> > > CPU0's tasklet queue remotely, then interrupting it.
> > As stop_machine_run() is scheduling a tasklet on all other cpus it
> > doesn't really matter. In the end I don't really mind either way.
> I think any case where we can avoid assigning special meaning
> to CPU 0 is helpful. While we won't get to being able to offline
> the BSP any time soon, we shouldn't put more road blocks on the
> path there.
As I said: fine with me. Shall I resend or can this be done while
committing?


Juergen


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