linux-kernel - [PATCH v3 0/3] x86/fpu: Fix MXCSR handling and SSE component definition

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Message-Id: <20221005215357.1808-1-chang.seok.bae@intel.com>
Date:   Wed,  5 Oct 2022 14:53:54 -0700
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, avagin@...il.com,
        seanjc@...gle.com, chang.seok.bae@...el.com
Subject: [PATCH v3 0/3] x86/fpu: Fix MXCSR handling and SSE component definition

Hi all,

Changes from v2 [1]:
* Drop the changes in fpstate_clear_xstate_component().
* Massage the WARNING and the comment in xfeature_get_offset().

If the former function is called for any legacy state, the WARNING is
eventually emitted by the latter function in this call chain:
  fpstate_clear_xstate_component()
    -> get_xsave_addr()
      -> __raw_xsave_addr()
        -> xfeature_get_offset()
So, the change in the outer function (the old patch3) was considered as not
necessary.

Thanks Sean Christopherson for the feedback.

== Regression ==

Recently the XSTATE copy functions were unitized together [2]. At a glance,
this change appears to relapse the ptrace write on the MXCSR state when
the non-compacted format is used in the kernel.

But, this regression appears to root in the XSAVES-enabling code [3] that
introduced the XSTATE conversion along with the MXCSR mistreatment.

== MXCSR Hindsight ==

MXCSR is architecturally part of the SSE component. The MXCSR association
of XSTATE_BV depends on the XSAVE format.

The change [3], however, presumed MXCSR as part of the X87 component and
made the kernel referencing XSTATE_BV regardless of the format.

== Patches ==

* Fix the MXCSR conversion code along with adding the test case.
* The hard-coded legacy state offset and size are adjusted in the end. And
  add a WARN when they are referenced.

These patches can be also found in this repository:
  git://github.com/intel/amx-linux.git mxcsr

Thanks,
Chang

[1] v2: https://lore.kernel.org/lkml/20220922200034.23759-1-chang.seok.bae@intel.com/
[2] Commit 43be46e89698 ("x86/fpu: Sanitize xstateregs_set()")
[3] Commit 91c3dba7dbc1 ("x86/fpu/xstate: Fix PTRACE frames for XSAVES")

Chang S. Bae (3):
  x86/fpu: Fix the MXCSR state reshuffling between userspace and kernel
    buffers
  selftests/x86/mxcsr: Test the MXCSR state write via ptrace
  x86/fpu: Correct the legacy state offset and size information

 arch/x86/kernel/fpu/xstate.c         |  89 ++++++++----
 tools/testing/selftests/x86/Makefile |   2 +-
 tools/testing/selftests/x86/mxcsr.c  | 200 +++++++++++++++++++++++++++
 3 files changed, 262 insertions(+), 29 deletions(-)
 create mode 100644 tools/testing/selftests/x86/mxcsr.c

base-commit: 03c739a21613a1a85f730dd972ff928e573f7235
-- 
2.17.1