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Re: [Qemu-devel] [PATCH v6 13/19] cputlb: atomically update tlb fields u

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH v6 13/19] cputlb: atomically update tlb fields used by tlb_reset_dirty
Date: Thu, 10 Nov 2016 19:32:59 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

On 11/10/2016 07:00 PM, Alex Bennée wrote:
I should probably expand that to default to false in the case of (sizeof
target_ulong > sizeof void *) when we don't have CONFIG_ATOMIC64.

Then if the user does force mttcg on they will quickly get an assert
although maybe we want to report that in a nicer way?

While forcing mttcg is good for testing, small hosts will definitely fail, so there's not point in even trying. We should report it in a nicer way.

We shouldn't be checking sizeof(void*), but checking TCG_TARGET_REG_BITS. That says how wide the host registers actually are, as opposed to the memory model in effect -- think x86_64 in x32 mode and the like.

If the host register size is smaller than the guest register size, we should force disable mttcg, regardles of CONFIG_ATOMIC64, because e.g. normal 64 bit loads and stores won't be atomic.


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