linux-kernel - Re: [PATCH v2 1/2] cxl/cdat: Handle cdat table build errors

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Message-ID: <659c1d888a5fc_8737f29495@iweiny-mobl.notmuch>
Date: Mon, 8 Jan 2024 08:06:32 -0800
From: Ira Weiny <ira.weiny@...el.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>, Ira Weiny
	<ira.weiny@...el.com>
CC: fan <nifan.cxl@...il.com>, Dave Jiang <dave.jiang@...el.com>,
	<linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Huai-Cheng Kuo
	<hchkuo@...ry-design.com.tw>
Subject: Re: [PATCH v2 1/2] cxl/cdat: Handle cdat table build errors

Jonathan Cameron wrote:
> On Wed, 20 Dec 2023 11:55:33 -0800
> Ira Weiny <ira.weiny@...el.com> wrote:
> 
> > fan wrote:
> > > On Wed, Nov 29, 2023 at 05:33:03PM -0800, Ira Weiny wrote:  
> > > > The callback for building CDAT tables may return negative error codes.
> > > > This was previously unhandled and will result in potentially huge
> > > > allocations later on in ct3_build_cdat()
> > > > 
> > > > Detect the negative error code and defer cdat building.
> > > > 
> > > > Fixes: f5ee7413d592 ("hw/mem/cxl-type3: Add CXL CDAT Data Object Exchange")
> > > > Cc: Huai-Cheng Kuo <hchkuo@...ry-design.com.tw>
> > > > Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> > > > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> > > > ---
> > > >  hw/cxl/cxl-cdat.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/hw/cxl/cxl-cdat.c b/hw/cxl/cxl-cdat.c
> > > > index 639a2db3e17b..24829cf2428d 100644
> > > > --- a/hw/cxl/cxl-cdat.c
> > > > +++ b/hw/cxl/cxl-cdat.c
> > > > @@ -63,7 +63,7 @@ static void ct3_build_cdat(CDATObject *cdat, Error **errp)
> > > >      cdat->built_buf_len = cdat->build_cdat_table(&cdat->built_buf,
> > > >                                                   cdat->private);
> > > >  
> > > > -    if (!cdat->built_buf_len) {
> > > > +    if (cdat->built_buf_len <= 0) {
> > > >          /* Build later as not all data available yet */
> > > >          cdat->to_update = true;
> > > >          return;
> > > >   
> > > 
> > > The fix looks good to me. Just curious how to really build cdat table
> > > again when an error occurs, for example, the memory allocation fails.  
> > 
> > I did not go that far as I am unsure as well.
> Memory allocations in qemu don't fail (well if they do it crashes)
> Side effect of using glib which makes for simpler cases.
> https://docs.gtk.org/glib/func.malloc.html
> 
> There shouldn't even be any checks :(  I'll fix that up at somepoint
> across all the CXL emulation.  Sometimes reviewers noticed and
> we dropped it at earlier stages, but clearly didn't catch them all.
> 
> Which come to think of it is why this error condition is in practice
> not actually buggy as the code won't ever manage to return -ENOMEM and
> I don't think there are other error codes.

Ah.  Ok but in that case I would say that build_cdat_table() should never
return < 0 to be clear at this level what can happen.

Would you like a patch for that?  (/me assumes you dropped this patch)

Ira