linux-kernel - [patch 0/3] x86/fpu/xsave: Add XSAVEC support and XGETBV1 utilization

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Date:   Mon,  4 Apr 2022 14:11:23 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Andrew Cooper <andrew.cooper3@...rix.com>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>
Subject: [patch 0/3] x86/fpu/xsave: Add XSAVEC support and XGETBV1 utilization

This series adds:

  1) XSAVEC support

     Hypervisors expose XSAVEC but not XSAVES to guests, but the kernel
     does not support XSAVEC. Which means it cannot make use of the
     compacted storage format.

  2) Utilize XGETBV1

     XGETBV1 reads a bitmap which contains the current active XSTATE
     components. This bitmap can be used to optimize the behaviour of
     XSAVES and XSAVEC by requesting only the active components to be
     saved.

     While the init optimization of XSAVEC and XSAVES skips writing the
     state of components which are inactive, the buffer layout is still
     providing the space for the inactive, but requested to save
     components. Which is suboptimal in terms of prefetch and dTLB when
     the active component bitmap is sparse.

Thanks,

	tglx
---
 include/asm/cpufeatures.h |    2 
 kernel/fpu/xstate.c       |  145 +++++++++++++++++++++++++++++++++++++---------
 kernel/fpu/xstate.h       |   42 ++++++++++---
 3 files changed, 152 insertions(+), 37 deletions(-)