Re: [PATCH] target/ppc: fix Hash64 MMU update of PTE bit R

[Daniel Henrique Barboza]

On 11/24/21 09:00, Leandro Lupori wrote:
> When updating the R bit of a PTE, the Hash64 MMU was using a wrong byte
> offset, causing the first byte of the adjacent PTE to be corrupted.
> This caused a panic when booting FreeBSD, using the Hash MMU.

If you add a "Fixes:" tag with the commit that introduced the code you're
fixing, we can push it right away as a bug fix in 6.2 (assuming it doesn't
break anything else, of course).

The commit to be fixed in the case seems to be a2dd4e83e76b ("ppc/hash64:
Rework R and C bit updates")

One more comment below:

> Signed-off-by: Leandro Lupori <leandro.lupori@eldorado.org.br>
> ---
>   target/ppc/mmu-hash64.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target/ppc/mmu-hash64.c b/target/ppc/mmu-hash64.c
> index 19832c4b46..f165ac691a 100644
> --- a/target/ppc/mmu-hash64.c
> +++ b/target/ppc/mmu-hash64.c
> @@ -786,7 +786,7 @@ static void ppc_hash64_set_dsi(CPUState *cs, int mmu_idx, 
> uint64_t dar, uint64_t
>   
>   static void ppc_hash64_set_r(PowerPCCPU *cpu, hwaddr ptex, uint64_t pte1)
>   {
> -    hwaddr base, offset = ptex * HASH_PTE_SIZE_64 + 16;
> +    hwaddr base, offset = ptex * HASH_PTE_SIZE_64 + 14;

Instead of adding a '14' you should add a new #define in mmu-hash64.h with this
value, something like "HPTE64_R_R_SHIFT". This will avoid hardcoding literals
around the code and forcing us to go to the ISA every time we wonder what's
an apparently random number represents. There's also a "HPTE64_R_R" defined
there but I'm not sure if it's usable here, so feel free to create a new
macro if needed.

In that note, the original commit that added this code also added a lot of
hardcoded "15" values for the C bit update in spapr_hpte_set_c() and
ppc_hash64_set_c(), and a "14" value like you're changing here in 
spapr_hpte_set_r().
If you're feeling generous I believe that another patch replacing these 
hardcoded values
with bit shift macros is warranted as well.


Thanks,


Daniel

>   
>       if (cpu->vhyp) {
>           PPCVirtualHypervisorClass *vhc =