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From: David Hildenbrand <david@redhat.com>
To: Richard Henderson <richard.henderson@linaro.org>, qemu-devel@nongnu.org
Cc: Thomas Huth <thuth@redhat.com>, Cornelia Huck <cohuck@redhat.com>,
	Riku Voipio <riku.voipio@iki.fi>,
	qemu-s390x@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>,
	Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] [PATCH v1 1/2] tcg: Make probe_write() return a pointer to the host page
Date: Wed, 28 Aug 2019 22:34:46 +0200	[thread overview]
Message-ID: <d3fad340-1ed1-fa9c-483f-7762b423d564@redhat.com> (raw)
In-Reply-To: <07f892a0-c8d8-9960-1536-082121cf2618@linaro.org>

On 28.08.19 16:44, Richard Henderson wrote:
> On 8/28/19 4:10 AM, David Hildenbrand wrote:
>> + * If the access is permitted, returns the host address similar to
>> + * tlb_vaddr_to_host(). Returns NULL in case direct access to the host page
>> + * is not allowed or if the size is 0.
> 
> Maybe we can find some better language -- "not allowed" sounds like a
> permissions check, and we longjmp out on permission check failures.
> 
> Perhaps "if the page requires i/o access"?

Yeah, and NOTDIRTY, emulated via i/o access. I will rephrase.

> 
> Why are you returning NULL for size 0?  Just because the caller hasn't
> committed to a size and thus we haven't checked watchpoints?

Yes, I think it's the right thing to do. Watchpoints are one part of the
story, the other part is TLB_RECHECK (a.k.a. TLB_INVALID_MASK or
"subpage protection"). Allowing access could lead to hidden BUGs.

I consider somebody wanting to get access to a host page with an access
size of zero an interface violation.

-- 

Thanks,

David / dhildenb


  reply	other threads:[~2019-08-28 20:57 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-28 11:10 [Qemu-devel] [PATCH v1 0/2] tcg: Introduce probe_access() and return a host pointer David Hildenbrand
2019-08-28 11:10 ` [Qemu-devel] [PATCH v1 1/2] tcg: Make probe_write() return a pointer to the host page David Hildenbrand
2019-08-28 14:44   ` Richard Henderson
2019-08-28 20:34     ` David Hildenbrand [this message]
2019-08-28 11:10 ` [Qemu-devel] [PATCH v1 2/2] tcg: Factor out probe_write() logic into probe_access() David Hildenbrand
2019-08-28 14:52   ` Richard Henderson
2019-08-28 20:30     ` David Hildenbrand

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