Re: [PATCH RFC v1] hw/i386: place setup_data at fixed place in memory

From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: qemu-devel@nongnu.org, "Xiaoyao Li" <xiaoyao.li@intel.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Richard Henderson" <richard.henderson@linaro.org>,
	"Peter Maydell" <peter.maydell@linaro.org>,
	"Daniel P . Berrangé" <berrange@redhat.com>,
	"Gerd Hoffmann" <kraxel@redhat.com>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	linux-efi@vger.kernel.org
Subject: Re: [PATCH RFC v1] hw/i386: place setup_data at fixed place in memory
Date: Thu, 4 Aug 2022 02:39:48 +0200	[thread overview]
Message-ID: <YusVVLNbLgsk49PK@zx2c4.com> (raw)
In-Reply-To: <Yur7ypNrSv8eO9/Q@zx2c4.com>

Hey again,

On Thu, Aug 04, 2022 at 12:50:50AM +0200, Jason A. Donenfeld wrote:
> Hi Michael,
> 
> On Wed, Aug 03, 2022 at 06:25:39PM -0400, Michael S. Tsirkin wrote:
> > > -    /* Offset 0x250 is a pointer to the first setup_data link. */
> > > -    stq_p(header + 0x250, first_setup_data);
> > > +    if (first_setup_data) {
> > > +            /* Offset 0x250 is a pointer to the first setup_data link. */
> > > +            stq_p(header + 0x250, first_setup_data);
> > > +            rom_add_blob("setup_data", setup_datas, setup_data_total_len, setup_data_total_len,
> > > +                         SETUP_DATA_PHYS_BASE, NULL, NULL, NULL, NULL, false);
> > > +    }
> > > +
> > >
> > 
> > Allocating memory on x86 is tricky business.  Can we maybe use bios-linker-loader
> > with COMMAND_WRITE_POINTER to get an address from firmware?
> 
> Hmm. Is BIOSLinker even available to us at this stage in preparation?
> 
> One thing to note is that this memory doesn't really need to be
> persistent. It's only used extreeeemely early in boot. So it could be
> somewhere that gets used/remapped later on.

Actually, it's possible there's one place that's already available, and
that this isn't so bad after all. In my tests, this seems to be working
in a wide variety of configurations. I'll send a v2.

Jason