[RESEND PATCH v2] powerpc/mce: Fix SLB rebolting during MCE recovery path.

[Michael Ellerman]

Nicholas Piggin <npiggin at gmail.com> writes:
> On Thu, 23 Aug 2018 12:06:53 +0530
> Mahesh J Salgaonkar <mahesh at linux.vnet.ibm.com> wrote:
>> From: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
>> 
>> With the powerpc next commit e7e81847478 (powerpc/mce: Fix SLB rebolting
>> during MCE recovery path.), the SLB error recovery is broken. The new
>> change now does not add index value to RB[52-63] that selects the SLB
>> entry while rebolting, instead it assumes that the shadow save area
>> already have index embeded correctly in esid field. While all valid bolted
>> save areas do contain index value set correctly, there is a case where
>> 3rd (KSTACK_INDEX) entry for kernel stack does not embed index for NULL
>> esid entry. This patch fixes that.
>> 
>> Without this patch the SLB rebolt code overwrites the 1st entry of kernel
>> linear mapping and causes SLB recovery to fail.
>> 
>> Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
>> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
>> Reviewed-by: Nicholas Piggin <npiggin at gmail.com>
>
> Changelog just needs a little more work, maybe this?
>
>
> The commit e7e81847478 ("powerpc/64s: move machine check SLB flushing
> to mm/slb.c") introduced a bug in reloading bolted SLB entries. Unused
> bolted entries are stored with .esid=0 in the slb_shadow area, and
> that value is now used directly as the RB input to slbmte, which means
> the RB[52:63] index field is set to 0, which causes SLB entry 0 to be
> cleared.
>
> Fix this by storing the index bits in the unused bolted entries, which
> directs the slbmte to the right place.
>
> The SLB shadow area is also used by the hypervisor, but PAPR is okay
> with that, from LoPAPR v1.1, 14.11.1.3 SLB Shadow Buffer:
>
>   Note: SLB is filled sequentially starting at index 0
>   from the shadow buffer ignoring the contents of
>   RB field bits 52-63
>
> Fixes: e7e81847478 ("powerpc/64s: move machine check SLB flushing to
> mm/slb.c")

Yep I'll take that, thanks.

cheers