Re: [Qemu-devel] [PATCH v2 1/1] RISC-V: Workaround for critical mstatus.FS MTTCG bug

[Richard Henderson]

On 03/28/2018 08:42 AM, Michael Clark wrote:
> This change is a workaround for a bug where mstatus.FS
> is not correctly reporting dirty after operations that
> modify floating point registers. This a critical bug
> or RISC-V in QEMU as it results in floating point
> register file corruption when running SMP Linux due to
> task migration and possibly uniprocessor Linux if
> more than one process is using the FPU.
> 
> This workaround will return dirty if mstatus.FS is
> switched from off to initial or clean. According to
> the specification it is legal for an implementation
> to return only off, or dirty.
> 
> Cc: Palmer Dabbelt <address@hidden>
> Cc: Sagar Karandikar <address@hidden>
> Cc: Bastian Koppelmann <address@hidden>
> Cc: Peter Maydell <address@hidden>
> Cc: Alex Bennée <address@hidden>
> Cc: Richard Henderson <address@hidden>
> Cc: Philippe Mathieu-Daudé <address@hidden>
> Tested-by: Richard W.M. Jones <address@hidden>
> Signed-off-by: Michael Clark <address@hidden>
> ---
>  target/riscv/op_helper.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)

In case the more extensive fix waits until 2.13,

Reviewed-by: Richard Henderson <address@hidden>


r~