Re: [PATCH v7 33/61] target/ppc: Add a function to check for page protection bit

["Nicholas Piggin" <npiggin@gmail.com>]

On Mon May 13, 2024 at 9:28 AM AEST, BALATON Zoltan wrote:
> Checking if a page protection bit is set for a given access type is a
> common operation. Add a function to avoid repeating the same check at
> multiple places. As this relies on access type and page protection bit
> values having certain relation also add an assert to ensure that this
> assumption holds.
>
> Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
> ---
>  target/ppc/cpu_init.c    |  5 +++++
>  target/ppc/internal.h    | 23 +++++------------------
>  target/ppc/mmu-hash32.c  |  6 +++---
>  target/ppc/mmu-hash64.c  |  2 +-
>  target/ppc/mmu-radix64.c |  2 +-
>  target/ppc/mmu_common.c  | 26 +++++++++++++-------------
>  6 files changed, 28 insertions(+), 36 deletions(-)
>
> diff --git a/target/ppc/cpu_init.c b/target/ppc/cpu_init.c
> index 92c71b2a09..d3b92d9f0e 100644
> --- a/target/ppc/cpu_init.c
> +++ b/target/ppc/cpu_init.c
> @@ -7388,6 +7388,11 @@ static void ppc_cpu_class_init(ObjectClass *oc, void *data)
>  #ifndef CONFIG_USER_ONLY
>      cc->sysemu_ops = &ppc_sysemu_ops;
>      INTERRUPT_STATS_PROVIDER_CLASS(oc)->get_statistics = ppc_get_irq_stats;
> +
> +    /* check_prot_access_type relies on MMU access and PAGE bits relations */
> +    qemu_build_assert(MMU_DATA_LOAD == 0 && MMU_DATA_STORE == 1 &&
> +                      MMU_INST_FETCH == 2 && PAGE_READ == 1 &&
> +                      PAGE_WRITE == 2 && PAGE_EXEC == 4);
>  #endif
>  
>      cc->gdb_num_core_regs = 71;
> diff --git a/target/ppc/internal.h b/target/ppc/internal.h
> index 4a90dd2584..20fb2ec593 100644
> --- a/target/ppc/internal.h
> +++ b/target/ppc/internal.h
> @@ -234,27 +234,14 @@ void destroy_ppc_opcodes(PowerPCCPU *cpu);
>  void ppc_gdb_init(CPUState *cs, PowerPCCPUClass *ppc);
>  const gchar *ppc_gdb_arch_name(CPUState *cs);
>  
> -/**
> - * prot_for_access_type:
> - * @access_type: Access type
> - *
> - * Return the protection bit required for the given access type.
> - */
> -static inline int prot_for_access_type(MMUAccessType access_type)
> +#ifndef CONFIG_USER_ONLY
> +
> +/* Check if permission bit required for the access_type is set in prot */
> +static inline int check_prot_access_type(int prot, MMUAccessType access_type)
>  {
> -    switch (access_type) {
> -    case MMU_INST_FETCH:
> -        return PAGE_EXEC;
> -    case MMU_DATA_LOAD:
> -        return PAGE_READ;
> -    case MMU_DATA_STORE:
> -        return PAGE_WRITE;
> -    }
> -    g_assert_not_reached();
> +    return prot & (1 << access_type);

I checked and sadly gcc is not able to figure this out on its own yet,
so we'll go with it. Nice improvement.

Reivewed-by: Nicholas Piggin <npiggin@gmail.com>

>  }
>  
> -#ifndef CONFIG_USER_ONLY
> -
>  /* PowerPC MMU emulation */
>  
>  bool ppc_xlate(PowerPCCPU *cpu, vaddr eaddr, MMUAccessType access_type,
> diff --git a/target/ppc/mmu-hash32.c b/target/ppc/mmu-hash32.c
> index 3abaf16e78..1e8f1df0f0 100644
> --- a/target/ppc/mmu-hash32.c
> +++ b/target/ppc/mmu-hash32.c
> @@ -252,7 +252,7 @@ static bool ppc_hash32_direct_store(PowerPCCPU *cpu, target_ulong sr,
>      }
>  
>      *prot = key ? PAGE_READ | PAGE_WRITE : PAGE_READ;
> -    if (*prot & prot_for_access_type(access_type)) {
> +    if (check_prot_access_type(*prot, access_type)) {
>          *raddr = eaddr;
>          return true;
>      }
> @@ -403,7 +403,7 @@ bool ppc_hash32_xlate(PowerPCCPU *cpu, vaddr eaddr, MMUAccessType access_type,
>      if (env->nb_BATs != 0) {
>          raddr = ppc_hash32_bat_lookup(cpu, eaddr, access_type, protp, mmu_idx);
>          if (raddr != -1) {
> -            if (prot_for_access_type(access_type) & ~*protp) {
> +            if (!check_prot_access_type(*protp, access_type)) {
>                  if (guest_visible) {
>                      if (access_type == MMU_INST_FETCH) {
>                          cs->exception_index = POWERPC_EXCP_ISI;
> @@ -471,7 +471,7 @@ bool ppc_hash32_xlate(PowerPCCPU *cpu, vaddr eaddr, MMUAccessType access_type,
>  
>      prot = ppc_hash32_pte_prot(mmu_idx, sr, pte);
>  
> -    if (prot_for_access_type(access_type) & ~prot) {
> +    if (!check_prot_access_type(prot, access_type)) {
>          /* Access right violation */
>          qemu_log_mask(CPU_LOG_MMU, "PTE access rejected\n");
>          if (guest_visible) {
> diff --git a/target/ppc/mmu-hash64.c b/target/ppc/mmu-hash64.c
> index 0966422a55..d9626f6aab 100644
> --- a/target/ppc/mmu-hash64.c
> +++ b/target/ppc/mmu-hash64.c
> @@ -1097,7 +1097,7 @@ bool ppc_hash64_xlate(PowerPCCPU *cpu, vaddr eaddr, MMUAccessType access_type,
>      amr_prot = ppc_hash64_amr_prot(cpu, pte);
>      prot = exec_prot & pp_prot & amr_prot;
>  
> -    need_prot = prot_for_access_type(access_type);
> +    need_prot = check_prot_access_type(PAGE_RWX, access_type);
>      if (need_prot & ~prot) {
>          /* Access right violation */
>          qemu_log_mask(CPU_LOG_MMU, "PTE access rejected\n");
> diff --git a/target/ppc/mmu-radix64.c b/target/ppc/mmu-radix64.c
> index 395ce3b782..2c5ade5cea 100644
> --- a/target/ppc/mmu-radix64.c
> +++ b/target/ppc/mmu-radix64.c
> @@ -209,7 +209,7 @@ static bool ppc_radix64_check_prot(PowerPCCPU *cpu, MMUAccessType access_type,
>      }
>  
>      /* Check if requested access type is allowed */
> -    if (prot_for_access_type(access_type) & ~*prot) {
> +    if (!check_prot_access_type(*prot, access_type)) {
>          /* Page Protected for that Access */
>          *fault_cause |= access_type == MMU_INST_FETCH ? SRR1_NOEXEC_GUARD :
>                                                          DSISR_PROTFAULT;
> diff --git a/target/ppc/mmu_common.c b/target/ppc/mmu_common.c
> index 69f98b7d0e..6746a8ff6b 100644
> --- a/target/ppc/mmu_common.c
> +++ b/target/ppc/mmu_common.c
> @@ -114,11 +114,6 @@ static int pp_check(int key, int pp, int nx)
>      return access;
>  }
>  
> -static int check_prot(int prot, MMUAccessType access_type)
> -{
> -    return prot & prot_for_access_type(access_type) ? 0 : -2;
> -}
> -
>  int ppc6xx_tlb_getnum(CPUPPCState *env, target_ulong eaddr,
>                                      int way, int is_code)
>  {
> @@ -165,13 +160,14 @@ static int ppc6xx_tlb_pte_check(mmu_ctx_t *ctx, target_ulong pte0,
>              /* Keep the matching PTE information */
>              ctx->raddr = pte1;
>              ctx->prot = access;
> -            ret = check_prot(ctx->prot, access_type);
> -            if (ret == 0) {
> +            if (check_prot_access_type(ctx->prot, access_type)) {
>                  /* Access granted */
>                  qemu_log_mask(CPU_LOG_MMU, "PTE access granted !\n");
> +                ret = 0;
>              } else {
>                  /* Access right violation */
>                  qemu_log_mask(CPU_LOG_MMU, "PTE access rejected\n");
> +                ret = -2;
>              }
>          }
>      }
> @@ -339,12 +335,14 @@ static int get_bat_6xx_tlb(CPUPPCState *env, mmu_ctx_t *ctx,
>                      (virtual & 0x0001F000);
>                  /* Compute access rights */
>                  ctx->prot = prot;
> -                ret = check_prot(ctx->prot, access_type);
> -                if (ret == 0) {
> +                if (check_prot_access_type(ctx->prot, access_type)) {
>                      qemu_log_mask(CPU_LOG_MMU, "BAT %d match: r " HWADDR_FMT_plx
>                                    " prot=%c%c\n", i, ctx->raddr,
>                                    ctx->prot & PAGE_READ ? 'R' : '-',
>                                    ctx->prot & PAGE_WRITE ? 'W' : '-');
> +                    ret = 0;
> +                } else {
> +                    ret = -2;
>                  }
>                  break;
>              }
> @@ -561,9 +559,11 @@ static int mmu40x_get_physical_address(CPUPPCState *env, hwaddr *raddr,
>  check_perms:
>              /* Check from TLB entry */
>              *prot = tlb->prot;
> -            ret = check_prot(*prot, access_type);
> -            if (ret == -2) {
> +            if (check_prot_access_type(*prot, access_type)) {
> +                ret = 0;
> +            } else {
>                  env->spr[SPR_40x_ESR] = 0;
> +                ret = -2;
>              }
>              break;
>          }
> @@ -621,7 +621,7 @@ static int mmubooke_check_tlb(CPUPPCState *env, ppcemb_tlb_t *tlb,
>      } else {
>          *prot = (tlb->prot >> 4) & 0xF;
>      }
> -    if (*prot & prot_for_access_type(access_type)) {
> +    if (check_prot_access_type(*prot, access_type)) {
>          qemu_log_mask(CPU_LOG_MMU, "%s: good TLB!\n", __func__);
>          return 0;
>      }
> @@ -823,7 +823,7 @@ found_tlb:
>              *prot |= PAGE_EXEC;
>          }
>      }
> -    if (*prot & prot_for_access_type(access_type)) {
> +    if (check_prot_access_type(*prot, access_type)) {
>          qemu_log_mask(CPU_LOG_MMU, "%s: good TLB!\n", __func__);
>          return 0;
>      }