From: Richard Henderson <richard.henderson@linaro.org>
To: David Hildenbrand <david@redhat.com>, qemu-devel@nongnu.org
Cc: Florian Weimer <fweimer@redhat.com>,
Thomas Huth <thuth@redhat.com>, Cornelia Huck <cohuck@redhat.com>,
Stefano Brivio <sbrivio@redhat.com>,
qemu-s390x@nongnu.org, Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] [PATCH v1 2/4] s390x/tcg: Introduce probe_read_access()
Date: Wed, 21 Aug 2019 15:43:23 -0700 [thread overview]
Message-ID: <ba9c379e-28a6-eb02-7f42-64a8bf76e589@linaro.org> (raw)
In-Reply-To: <a8b1436d-a634-d767-8861-460c50acecb2@linaro.org>
On 8/21/19 3:31 PM, Richard Henderson wrote:
>> Yes, that's what I mean, TARGET_PAGE_SIZE, but eventually crossing a
>> page boundary. The longer I stare at the MVCL code, the more broken it
>> is. There are more nice things buried in the PoP. MVCL does not detect
>> access exceptions beyond the next 2k. So we have to limit it there
>> differently.
> That language is indeed odd.
>
> The only reading of that paragraph that makes sense to me is that the hardware
> *must* interrupt MVCL after every 2k bytes processed. The idea that the user
> can magically write to a read-only page simply by providing length = 2MB and
> page that is initially writable is dumb. I cannot imagine that is a correct
> reading.
>
> Getting clarification from an IBM engineer on that would be good; otherwise I
> would just ignore that and proceed as if all access checks are performed.
>
FWIW, splitting the operation at every aligned 2k boundary is exactly what the
Hercules emulator does:
len3 = NOCROSS2KL(addr1,len1) ? len1 : (int)(0x800 - (addr1 & 0x7FF));
len4 = NOCROSS2KL(addr2,len2) ? len2 : (int)(0x800 - (addr2 & 0x7FF));
len = len3 < len4 ? len3 : len4;
/* Use concpy to ensure Concurrent block update consistency */
concpy (regs, dest, source, len);
After this it writes back the lengths and addresses to the
register file, and then if necessary loops back to the address
translation step.
r~
next prev parent reply other threads:[~2019-08-21 22:44 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-21 9:22 [Qemu-devel] [PATCH v1 0/4] s390x/tcg: MOVE (MVC): Fault-safe handling David Hildenbrand
2019-08-21 9:22 ` [Qemu-devel] [PATCH v1 1/4] s390x/tcg: Use guest_addr_valid() instead of h2g_valid() in probe_write_access() David Hildenbrand
2019-08-21 9:22 ` [Qemu-devel] [PATCH v1 2/4] s390x/tcg: Introduce probe_read_access() David Hildenbrand
2019-08-21 17:26 ` Richard Henderson
2019-08-21 17:37 ` David Hildenbrand
2019-08-21 19:19 ` Richard Henderson
2019-08-21 19:36 ` David Hildenbrand
2019-08-21 20:38 ` Richard Henderson
2019-08-21 21:33 ` David Hildenbrand
2019-08-21 22:31 ` Richard Henderson
2019-08-21 22:43 ` Richard Henderson [this message]
2019-08-22 6:42 ` David Hildenbrand
2019-08-22 7:01 ` David Hildenbrand
2019-08-26 9:31 ` David Hildenbrand
2019-08-21 18:48 ` David Hildenbrand
2019-08-21 9:22 ` [Qemu-devel] [PATCH v1 3/4] s390x/tcg: MOVE (MVC): Increment the length once David Hildenbrand
2019-08-21 15:47 ` Richard Henderson
2019-08-21 9:22 ` [Qemu-devel] [PATCH v1 4/4] s390x/tcg: MOVE (MVC): Fault-safe handling David Hildenbrand
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