[PATCH v3 5/5] arm: qemu: override flash accessors to use virtualizable instructions

Tom Rini trini at konsulko.com
Wed Jul 29 15:44:02 CEST 2020

On Tue, Jul 07, 2020 at 12:07:11PM +0200, Ard Biesheuvel wrote:

> Some instructions in the ARM ISA have multiple output registers, such
> as ldrd/ldp (load pair), where two registers are loaded from memory,
> but also ldr with indexing, where the memory base register is incremented
> as well when the value is loaded to the destination register.
> MMIO emulation under KVM is based on using the architecturally defined
> syndrome information that is provided when an exception is taken to the
> hypervisor. This syndrome information describes whether the instruction
> that triggered the exception is a load or a store, what the faulting
> address was, and which register was the destination register.
> This syndrome information can only describe one destination register, and
> when the trapping instruction is one with multiple outputs, KVM throws an
> error like
>   kvm [615929]: Data abort outside memslots with no valid syndrome info
> on the host and kills the QEMU process with the following error:
>   U-Boot 2020.07-rc3-00208-g88bd5b179360-dirty (Jun 06 2020 - 11:59:22 +0200)
>   DRAM:  1 GiB
>   Flash: error: kvm run failed Function not implemented
>   R00=00000001 R01=00000040 R02=7ee0ce20 R03=00000000
>   R04=7ffd9eec R05=00000004 R06=7ffda3f8 R07=00000055
>   R08=7ffd9eec R09=7ef0ded0 R10=7ee0ce20 R11=00000000
>   R12=00000004 R13=7ee0cdf8 R14=00000000 R15=7ff72d08
>   PSR=200001d3 --C- A svc32
>   QEMU: Terminated
> This means that, in order to run U-Boot in QEMU under KVM, we need to
> avoid such instructions when accessing emulated devices. For the flash
> in particular, which is a hybrid between a ROM (backed by a read-only
> KVM memslot) when in array mode, and an emulated MMIO device (when in
> write mode), we need to take care to only use instructions that KVM can
> deal with when they trap.
> So override the flash read accessors that are used when running on QEMU
> under KVM. Note that the the 64-bit wide read and write accessors have
> been omitted: they are never used when running under QEMU given that it
> does not emulate CFI flash that supports it.
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> Reviewed-by: Andre Przywara <andre.przywara at arm.com>

Applied to u-boot/master, thanks!

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