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Re: [Qemu-devel] [PATCH v3] target/s390x: Add support for the TEST BLOCK


From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH v3] target/s390x: Add support for the TEST BLOCK instruction
Date: Thu, 18 May 2017 08:39:31 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0

On 05/18/2017 07:19 AM, Thomas Huth wrote:
TEST BLOCK was likely once used to execute basic memory
tests, but nowadays it is just a (slow) way to clear a page.

Signed-off-by: Thomas Huth <address@hidden>
---
  v3:
  - Use TCG_CALL_NO_RWG instead of TCG_CALL_NO_WG
  - Use potential_page_fault() since the helper can generate an exception

You were right the first time, using TCG_CALL_NO_WG, since an exception path implies that all of the register values are read (by being live values when we restart at the exception handler).

As an aside, we really should convert target/s390 to properly use cpu_loop_exit_restore so that we can drop potential_page_fault().


r~



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