On Mon, 2022-02-14 at 13:20 +1000, Nicholas Piggin wrote:
> Excerpts from Haren Myneni's message of January 22, 2022 5:58 am:
> > The paste address mapping is done with mmap() after the window is
> > opened with ioctl. But the window can be closed due to lost credit
> > due to core removal before mmap(). So if the window is not active,
> > return mmap() failure with -EACCES and expects the user space
> > reissue
> > mmap() when the window is active or open new window when the credit
> > is available.
> >
> > Signed-off-by: Haren Myneni <ha...@linux.ibm.com>
> > ---
> > arch/powerpc/platforms/book3s/vas-api.c | 21 ++++++++++++++++++++-
> > 1 file changed, 20 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/platforms/book3s/vas-api.c
> > b/arch/powerpc/platforms/book3s/vas-api.c
> > index a63fd48e34a7..2d06bd1b1935 100644
> > --- a/arch/powerpc/platforms/book3s/vas-api.c
> > +++ b/arch/powerpc/platforms/book3s/vas-api.c
> > @@ -379,10 +379,27 @@ static int coproc_mmap(struct file *fp,
> > struct vm_area_struct *vma)
> > return -EACCES;
> > }
> >
> > + /*
> > + * The initial mapping is done after the window is opened
> > + * with ioctl. But this window might have been closed
> > + * due to lost credit (core removal on PowerVM) before mmap().
>
> What does "initial mapping" mean?
>
> mapping ~= mmap, in kernel speak.
yes, the initial mapping is done with the actual mmap() call.
>
> You will have to differentiate the concepts.
>
> > + * So if the window is not active, return mmap() failure
> > + * with -EACCES and expects the user space reconfigure (mmap)
> > + * window when it is active again or open new window when
> > + * the credit is available.
> > + */
> > + mutex_lock(&txwin->task_ref.mmap_mutex);
> > + if (txwin->status != VAS_WIN_ACTIVE) {
> > + pr_err("%s(): Window is not active\n", __func__);
> > + rc = -EACCES;
> > + goto out;
> > + }
> > +
> > paste_addr = cp_inst->coproc->vops->paste_addr(txwin);
> > if (!paste_addr) {
> > pr_err("%s(): Window paste address failed\n",
> > __func__);
> > - return -EINVAL;
> > + rc = -EINVAL;
> > + goto out;
> > }
> >
> > pfn = paste_addr >> PAGE_SHIFT;
> > @@ -401,6 +418,8 @@ static int coproc_mmap(struct file *fp, struct
> > vm_area_struct *vma)
> >
> > txwin->task_ref.vma = vma;
> >
> > +out:
> > + mutex_unlock(&txwin->task_ref.mmap_mutex);
>
> If the hypervisor can revoke a window at any point with DLPAR, it's
> not
> clear *why* this is needed. The hypervisor could cause your window
> to
> close right after this mmap() returns, right? So an explanation for
> exactly what this patch is needed for beyond that would help.
Yes, the window can be closed by OS due to DLPAR after the mmap()
returns successfully which is a normal case - paste instruction failure
until the window is reopened again.
But ths patch is mainly for window open by user space and dlpar happens
before the user space issue mmap().
I will add more description in the commit log.
Thanks
Haren
>
> Thanks,
> Nick
