From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josh Triplett Subject: Re: [PATCH] efi-bgrt: Add error handling; inform the user when ignoring the BGRT Date: Tue, 5 Aug 2014 09:39:39 -0700 Message-ID: <20140805163932.GA3146@thin> References: <20140730192331.GA23730@jtriplet-mobl1> <20140731103110.GC15082@console-pimps.org> <20140731161133.GA12663@cloud> <20140801091949.GD15082@console-pimps.org> <20140801161154.GA1258@thin> <20140804121959.GG15082@console-pimps.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20140804121959.GG15082-HNK1S37rvNbeXh+fF434Mdi2O/JbrIOy@public.gmane.org> Sender: linux-efi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Matt Fleming Cc: Matt Fleming , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Srihari Vijayaraghavan , Andrew Morton , Matthew Garrett List-Id: linux-efi@vger.kernel.org On Mon, Aug 04, 2014 at 01:19:59PM +0100, Matt Fleming wrote: > On Fri, 01 Aug, at 09:11:54AM, Josh Triplett wrote: > > > > The original bug report was about an allocation failure for a fairly > > reasonable BGRT size. We can certainly prohibit absurdly huge ones (for > > instance, bigger than the maximum likely screen resolution times 4 bytes > > per pixel), but allocation failures may well occur for smaller sizes, > > and I don't think we want to spew a massive warning for that either. > > Oh, dammit, that's my bad. I misread the allocation size and thought it > was huge, but now realise it was only 6MB or so. Sorry Josh. > > I was worried that this was the first reported instance of a BGRT > claiming to be valid but with a bogusly large image size. I've never > been so happy to be wrong. :) > However, the fact that the allocation failed is worth investigating - > this machine appears to have GBs of ram. Perhaps we should switch to > requesting pages directly instead of relying on kmalloc()? > > I appreciate that the BGRT code isn't mission critical or anything like > that, and that failing the alloc isn't the end of the world, but if we > have code in the kernel it should really be as robust as possible. I > don't think trying to kmalloc() ~6MB can claim to be robust. vmalloc or flex_array could potentially help here. However, I'd suggest we go ahead and merge this patch to improve the existing error handling before doing a more extensive rewrite to use one of those. Would anything go horrifically wrong if this allocation used vmalloc? We really don't care deeply about the performance of this memory; it just needs a single copy in and a small number of copies out in the lifetime of a system. - Josh Triplett