Re: [PATCH v3] target/ppc: fix Hash64 MMU update of PTE bit R

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Nov 26, 2021 at 04:39:40PM -0300, 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.
> 
> Fixes: a2dd4e83e76b ("ppc/hash64: Rework R and C bit updates")
> Signed-off-by: Leandro Lupori <leandro.lupori@eldorado.org.br>
> ---
> Changes from v2:
> - Add new defines for the byte offset of PTE bit C and
>   HASH_PTE_SIZE_64 / 2 (pte1)
> - Use new defines in hash64 and spapr code
> ---
>  hw/ppc/spapr.c          | 8 ++++----
>  hw/ppc/spapr_softmmu.c  | 2 +-
>  target/ppc/mmu-hash64.c | 4 ++--
>  target/ppc/mmu-hash64.h | 5 +++++
>  4 files changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 163c90388a..8ebf85bad8 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1414,7 +1414,7 @@ void spapr_store_hpte(PowerPCCPU *cpu, hwaddr ptex,
>          kvmppc_write_hpte(ptex, pte0, pte1);
>      } else {
>          if (pte0 & HPTE64_V_VALID) {
> -            stq_p(spapr->htab + offset + HASH_PTE_SIZE_64 / 2, pte1);
> +            stq_p(spapr->htab + offset + HPTE64_R_BYTE_OFFSET, pte1);

Urgh.. so, initially I thought this was wrong because I was confusing
HPTE64_R_BYTE_OFFSET with HPTE64_R_R_BYTE_OFFSET.  I doubt I'd be the
only one.

Calling something a BYTE_OFFSET then doing an stq to it is pretty
misleading I think.  WORD1_OFFSET or R_WORD_OFFSET might be better?

Or you could change these writebacks to byte writes, as powernv has
already been changed.  I'm not sure if that's necessary in the case of
pseries - since in that case the HPT doesn't exist within the guest's
address space.

>              /*
>               * When setting valid, we write PTE1 first. This ensures
>               * proper synchronization with the reading code in
> @@ -1430,7 +1430,7 @@ void spapr_store_hpte(PowerPCCPU *cpu, hwaddr ptex,
>               * ppc_hash64_pteg_search()
>               */
>              smp_wmb();
> -            stq_p(spapr->htab + offset + HASH_PTE_SIZE_64 / 2, pte1);
> +            stq_p(spapr->htab + offset + HPTE64_R_BYTE_OFFSET, pte1);
>          }
>      }
>  }
> @@ -1438,7 +1438,7 @@ void spapr_store_hpte(PowerPCCPU *cpu, hwaddr ptex,
>  static void spapr_hpte_set_c(PPCVirtualHypervisor *vhyp, hwaddr ptex,
>                               uint64_t pte1)
>  {
> -    hwaddr offset = ptex * HASH_PTE_SIZE_64 + 15;
> +    hwaddr offset = ptex * HASH_PTE_SIZE_64 + HPTE64_R_C_BYTE_OFFSET;
>      SpaprMachineState *spapr = SPAPR_MACHINE(vhyp);
>  
>      if (!spapr->htab) {
> @@ -1454,7 +1454,7 @@ static void spapr_hpte_set_c(PPCVirtualHypervisor *vhyp, hwaddr ptex,
>  static void spapr_hpte_set_r(PPCVirtualHypervisor *vhyp, hwaddr ptex,
>                               uint64_t pte1)
>  {
> -    hwaddr offset = ptex * HASH_PTE_SIZE_64 + 14;
> +    hwaddr offset = ptex * HASH_PTE_SIZE_64 + HPTE64_R_R_BYTE_OFFSET;
>      SpaprMachineState *spapr = SPAPR_MACHINE(vhyp);
>  
>      if (!spapr->htab) {
> diff --git a/hw/ppc/spapr_softmmu.c b/hw/ppc/spapr_softmmu.c
> index f8924270ef..03676c4448 100644
> --- a/hw/ppc/spapr_softmmu.c
> +++ b/hw/ppc/spapr_softmmu.c
> @@ -426,7 +426,7 @@ static void new_hpte_store(void *htab, uint64_t pteg, int slot,
>      addr += slot * HASH_PTE_SIZE_64;
>  
>      stq_p(addr, pte0);
> -    stq_p(addr + HASH_PTE_SIZE_64 / 2, pte1);
> +    stq_p(addr + HPTE64_R_BYTE_OFFSET, pte1);
>  }
>  
>  static int rehash_hpte(PowerPCCPU *cpu,
> diff --git a/target/ppc/mmu-hash64.c b/target/ppc/mmu-hash64.c
> index 19832c4b46..168d397c26 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 + HPTE64_R_R_BYTE_OFFSET;
>  
>      if (cpu->vhyp) {
>          PPCVirtualHypervisorClass *vhc =
> @@ -803,7 +803,7 @@ static void ppc_hash64_set_r(PowerPCCPU *cpu, hwaddr ptex, uint64_t pte1)
>  
>  static void ppc_hash64_set_c(PowerPCCPU *cpu, hwaddr ptex, uint64_t pte1)
>  {
> -    hwaddr base, offset = ptex * HASH_PTE_SIZE_64 + 15;
> +    hwaddr base, offset = ptex * HASH_PTE_SIZE_64 + HPTE64_R_C_BYTE_OFFSET;
>  
>      if (cpu->vhyp) {
>          PPCVirtualHypervisorClass *vhc =
> diff --git a/target/ppc/mmu-hash64.h b/target/ppc/mmu-hash64.h
> index c5b2f97ff7..2a46763f70 100644
> --- a/target/ppc/mmu-hash64.h
> +++ b/target/ppc/mmu-hash64.h
> @@ -97,6 +97,11 @@ void ppc_hash64_finalize(PowerPCCPU *cpu);
>  #define HPTE64_V_1TB_SEG        0x4000000000000000ULL
>  #define HPTE64_V_VRMA_MASK      0x4001ffffff000000ULL
>  
> +/* PTE byte offsets */
> +#define HPTE64_R_R_BYTE_OFFSET  14
> +#define HPTE64_R_C_BYTE_OFFSET  15
> +#define HPTE64_R_BYTE_OFFSET    (HASH_PTE_SIZE_64 / 2)
> +
>  /* Format changes for ARCH v3 */
>  #define HPTE64_V_COMMON_BITS    0x000fffffffffffffULL
>  #define HPTE64_R_3_0_SSIZE_SHIFT 58

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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