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Re: [Qemu-devel] [PATCH 26/26] tcg: Use tlb_fill probe from tlb_vaddr_to

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH 26/26] tcg: Use tlb_fill probe from tlb_vaddr_to_host
Date: Wed, 8 May 2019 22:24:17 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

On 4/29/19 10:41 AM, Peter Maydell wrote:
> On Wed, 3 Apr 2019 at 05:05, Richard Henderson
> <address@hidden> wrote:
>> Most of the existing users would continue around a loop which
>> would fault the tlb entry in via a normal load/store.  But for
>> SVE we have a true non-faulting case which requires the new
>> probing form of tlb_fill.
> So am I right in thinking that this fixes a bug where we
> previously would mark a load as faulted if the memory happened
> not to be in the TLB, whereas now we will correctly pull in the
> TLB entry and do the load ?


> (Since guest code ought to be handling the "non-first-load
> faulted" case by looping round or otherwise arranging to
> retry, nothing in practice would have noticed this bug, right?)


The only case with changed behaviour is (expected to be) SVE no-fault, where
the loop you mention would have produced different incorrect results.


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