Re: [PATCH kvmtool v3] Add emulation for CFI compatible flash memory

From: Will Deacon <will@kernel.org>
To: Andre Przywara <andre.przywara@arm.com>
Cc: kvm@vger.kernel.org, Raphael Gault <raphael.gault@arm.com>,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Sami Mujawar <sami.mujawar@arm.com>,
	Alexandru Elisei <Alexandru.Elisei@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH kvmtool v3] Add emulation for CFI compatible flash memory
Date: Wed, 18 Mar 2020 21:58:47 +0000	[thread overview]
Message-ID: <20200318215847.GC8477@willie-the-truck> (raw)
In-Reply-To: <20200221165532.90618-1-andre.przywara@arm.com>

On Fri, Feb 21, 2020 at 04:55:32PM +0000, Andre Przywara wrote:
> From: Raphael Gault <raphael.gault@arm.com>
> 
> The EDK II UEFI firmware implementation requires some storage for the EFI
> variables, which is typically some flash storage.
> Since this is already supported on the EDK II side, we add a CFI flash
> emulation to kvmtool.
> This is backed by a file, specified via the --flash or -F command line
> option. Any flash writes done by the guest will immediately be reflected
> into this file (kvmtool mmap's the file).
> The flash will be limited to the nearest power-of-2 size, so only the
> first 2 MB of a 3 MB file will be used.
> 
> This implements a CFI flash using the "Intel/Sharp extended command
> set", as specified in:
> - JEDEC JESD68.01
> - JEDEC JEP137B
> - Intel Application Note 646
> Some gaps in those specs have been filled by looking at real devices and
> other implementations (QEMU, Linux kernel driver).
> 
> At the moment this relies on DT to advertise the base address of the
> flash memory (mapped into the MMIO address space) and is only enabled
> for ARM/ARM64. The emulation itself is architecture agnostic, though.
> 
> This is one missing piece toward a working UEFI boot with kvmtool on
> ARM guests, the other is to provide writable PCI BARs, which is WIP.
> 
> Signed-off-by: Raphael Gault <raphael.gault@arm.com>
> [Andre: rewriting and fixing]
> Signed-off-by: Andre Przywra <andre.przywara@arm.com>
> ---
> Hi,
> 
> an update fixing Alexandru's review comments (many thanks for those!)
> The biggest change code-wise is the split of the MMIO handler into three
> different functions. Another significant change is the rounding *down* of
> the present flash file size to the nearest power-of-two, to match flash
> hardware chips and Linux' expectations.

Alexandru -- are you happy with this now?

Will

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