Re: [PATCH v2 2/4] s390x/tcg: Fix RISBHG

[Richard Henderson]

On 1/8/21 3:20 AM, David Hildenbrand wrote:
> RISBHG is broken and currently hinders clang-11 builds of upstream kernels
> from booting: the kernel crashes early, while decompressing the image.
> 
>   [...]
>    Kernel fault: interruption code 0005 ilc:2
>    Kernel random base: 0000000000000000
>    PSW : 0000200180000000 0000000000017a1e
>          R:0 T:0 IO:0 EX:0 Key:0 M:0 W:0 P:0 AS:0 CC:2 PM:0 RI:0 EA:3
>    GPRS: 0000000000000001 0000000c00000000 00000003fffffff4 00000000fffffff0
>          0000000000000000 00000000fffffff4 000000000000000c 00000000fffffff0
>          00000000fffffffc 0000000000000000 00000000fffffff8 00000000008e25a8
>          0000000000000009 0000000000000002 0000000000000008 000000000000bce0
> 
> One example of a buggy instruction is:
> 
>     17dde:       ec 1e 00 9f 20 5d       risbhg  %r1,%r14,0,159,32
> 
> With %r14 = 0x9 and %r1 = 0x7 should result in %r1 = 0x900000007, however,
> results in %r1 = 0.
> 
> Let's interpret values of i3/i4 as documented in the PoP and make
> computation of "mask" only based on i3 and i4 and use "pmask" only at the
> very end to make sure wrapping is only applied to the high/low doubleword.
> 
> With this patch, I can successfully boot a v5.11-rc2 kernel built with
> clang-11, and gcc builds keep on working.
> 
> Fixes: 2d6a869833d9 ("target-s390: Implement RISBG")
> Reported-by: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Guenter Roeck <linux@roeck-us.net>
> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  target/s390x/translate.c | 18 ++++++++----------
>  1 file changed, 8 insertions(+), 10 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~