Re: [PATCH v3] hw/i386: place setup_data at fixed place in memory

From: Paolo Bonzini <pbonzini@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "Ard Biesheuvel" <ardb@kernel.org>,
	"Jason A. Donenfeld" <Jason@zx2c4.com>,
	qemu-devel@nongnu.org, "Xiaoyao Li" <xiaoyao.li@intel.com>,
	"Richard Henderson" <richard.henderson@linaro.org>,
	"Peter Maydell" <peter.maydell@linaro.org>,
	"Daniel P. Berrangé" <berrange@redhat.com>,
	"Gerd Hoffmann" <kraxel@redhat.com>,
	"Laszlo Ersek" <lersek@redhat.com>,
	linux-efi@vger.kernel.org
Subject: Re: [PATCH v3] hw/i386: place setup_data at fixed place in memory
Date: Tue, 9 Aug 2022 16:19:18 +0200	[thread overview]
Message-ID: <50215d9d-0a72-dea1-30dd-6abec36b0c14@redhat.com> (raw)
In-Reply-To: <20220809051644-mutt-send-email-mst@kernel.org>

On 8/9/22 11:17, Michael S. Tsirkin wrote:
>> 1) if we believe "build setup_data in QEMU" is a feasible design that only
>> needs more yak shaving, we can keep the code in, but disabled by default,
>> and sort it out in 7.2.
>>
>> 2) if we go for an alternative design, it needs to be reverted.  For example
>> the randomness could be in _another_ fw_cfg file, and the linuxboot DMA can
>> patch it in the setup_data.
>>
>> With (2) the OVMF breakage would be limited to -dtb, which more or less
>> nobody cares about, and we can just look the other way.
> 
> So IIUC you retract your pc: add property for Linux setup_data random
> number seed then? It's neither of the two options above.

That one would be a base for (1).

Another choice (3) is to put a pointer to the first setup_data in a new 
fw_cfg entry, and let the option ROMs place it in the header.

In any case, as Laszlo said this [PATCH v3] does not work because 
0xf0000 is mapped as ROM (and if it worked, it would have the same 
problem as the first 640K).

Paolo