linux-kernel - [PATCH v2 0/2] riscv: Correct the initialized flow of FP and __fstate

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Message-Id: <1565771033-1831-1-git-send-email-vincent.chen@sifive.com>
Date:   Wed, 14 Aug 2019 16:23:51 +0800
From:   Vincent Chen <vincent.chen@...ive.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...ive.com>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Vincent Chen <vincent.chen@...ive.com>
Subject: [PATCH v2 0/2] riscv: Correct the initialized flow of FP and __fstate_clean()

The following two reasons cause FP registers are sometimes not
initialized before starting the user program.
1. Currently, the FP context is initialized in flush_thread() function
   and we expect these initial values to be restored to FP register when
   doing FP context switch. However, the FP context switch only occurs in
   switch_to function. Hence, if this process does not be scheduled out
   and scheduled in before entering the user space, the FP registers
   have no chance to initialize.
2. In flush_thread(), the state of reg->sstatus.FS inherits from the
   parent. Hence, the state of reg->sstatus.FS may be dirty. If this
   process is scheduled out during flush_thread() and initializing the
   FP register, the fstate_save() in switch_to will corrupt the FP context
   which has been initialized until flush_thread().
In addition, the __fstate_clean() function cannot correctly set the state
of sstatus.FS to SR_FS_CLEAN. These problems will be solved in this patch
set.

Changes since v1:
- Remove unneeded braces
- Remove unneeded ifdef condition
- Make the correction for __fstate_clean() be a RC fix

Vincent Chen (2):
  riscv: Correct the initialized flow of FP register
  riscv: Make __fstate_clean() work correctly.

 arch/riscv/include/asm/switch_to.h |  8 +++++++-
 arch/riscv/kernel/process.c        | 11 +++++++++--
 2 files changed, 16 insertions(+), 3 deletions(-)

-- 
2.7.4