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Re: [Qemu-devel] [PULL 3/5] exec: Support 64-bit operations in address_s
From: |
Richard Henderson |
Subject: |
Re: [Qemu-devel] [PULL 3/5] exec: Support 64-bit operations in address_space_rw |
Date: |
Wed, 17 Jul 2013 06:23:45 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 |
On 07/17/2013 04:09 AM, Paolo Bonzini wrote:
>>
>> Fails for me:
>>
>> qemu-system-x86_64: /work/armbru/qemu/exec.c:1927: memory_access_size:
>> Assertion `l >= access_size_min' failed.
>
> This:
>
> unsigned access_size_min = mr->ops->impl.min_access_size;
> unsigned access_size_max = mr->ops->impl.max_access_size;
>
> must be respectively:
>
> unsigned access_size_min = 1;
> unsigned access_size_max = mr->ops->valid.max_access_size;
>
> access_size_min can be 1 because erroneous accesses must not crash
> QEMU, they should trigger exceptions in the guest or just return
> garbage (depending on the CPU). I'm not sure I understand the comment,
> placing a 4-byte field at the last byte of a region makes no sense
> (unless impl.unaligned is true).
>
> access_size_max can be mr->ops->valid.max_access_size because memory.c
> can and will still break accesses bigger than
> mr->ops->impl.max_access_size.
>
> Markus, can you try the minimal patch above? Or this one that also
> does the consequent simplifications.
NAK.
If you remove the check here, you're just trading it for one in the device.
The device told you that it can't support a 1 byte read. (Either that, or the
device incorrectly reported what it can actually do.)
The proper fix is to change the interface of memory_access_size such that it
can report errors. Indeed, very likely we should change it and its callers to
also support over-sized reads, like access_with_adjusted_size in memory.c.
r~
- [Qemu-devel] [PULL 0/5] alpha-softmmu fixes, Richard Henderson, 2013/07/14
- Re: [Qemu-devel] [PULL 3/5] exec: Support 64-bit operations in address_space_rw, Anthony Liguori, 2013/07/17
- Re: [Qemu-devel] [PULL 3/5] exec: Support 64-bit operations in address_space_rw, Paolo Bonzini, 2013/07/17
- Re: [Qemu-devel] [PULL 3/5] exec: Support 64-bit operations in address_space_rw, Richard Henderson, 2013/07/17
- Re: [Qemu-devel] [PULL 3/5] exec: Support 64-bit operations in address_space_rw, Paolo Bonzini, 2013/07/17
- Re: [Qemu-devel] [PULL 3/5] exec: Support 64-bit operations in address_space_rw, Richard Henderson, 2013/07/17
- Re: [Qemu-devel] [PULL 3/5] exec: Support 64-bit operations in address_space_rw, Paolo Bonzini, 2013/07/17
- Re: [Qemu-devel] [PULL 3/5] exec: Support 64-bit operations in address_space_rw, Richard Henderson, 2013/07/17