Re: [PATCH v3 33/33] target/ppc: Add a macro to check for page protection bit

[BALATON Zoltan]

On Wed, 8 May 2024, Nicholas Piggin wrote:
> On Wed May 8, 2024 at 10:15 AM AEST, BALATON Zoltan wrote:
> > Checking if a page protection bit is set for a given access type is a
> > common operation. Add a macro to avoid repeating the same check at
> > multiple places and also avoid a function call. 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    |  4 ++++
> >  target/ppc/internal.h    | 20 ++------------------
> >  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, 24 insertions(+), 36 deletions(-)
> >
> > diff --git a/target/ppc/cpu_init.c b/target/ppc/cpu_init.c
> > index 92c71b2a09..6639235544 100644
> > --- a/target/ppc/cpu_init.c
> > +++ b/target/ppc/cpu_init.c
> > @@ -7377,6 +7377,10 @@ static void ppc_cpu_class_init(ObjectClass *oc, void 
> > *data)
> >      resettable_class_set_parent_phases(rc, NULL, ppc_cpu_reset_hold, NULL,
> >                                         &pcc->parent_phases);
> >
> > +    /* CHECK_PROT_ACCESS relies on this MMU access and PAGE bits relation */
> > +    assert(MMU_DATA_LOAD == 0 && MMU_DATA_STORE == 1 && MMU_INST_FETCH == 2 &&
> > +           PAGE_READ == 1 && PAGE_WRITE == 2 && PAGE_EXEC == 4);
> > +
>
> Can you use qemu_build_assert() for this?

First I've try #if and #error but seems access_type is an enum and the 
preprocessor does not see those. If qemu_build_assert is a wrapper around 
the same then it might not work but I'll check.

> >      cc->class_by_name = ppc_cpu_class_by_name;
> >      cc->has_work = ppc_cpu_has_work;
> >      cc->mmu_index = ppc_cpu_mmu_index;
> > diff --git a/target/ppc/internal.h b/target/ppc/internal.h
> > index 46176c4711..9880422ce3 100644
> > --- a/target/ppc/internal.h
> > +++ b/target/ppc/internal.h
> > @@ -234,24 +234,8 @@ 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)
> > -{
> > -    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();
> > -}
> > +/* Check if permission bit required for the access_type is set in prot */
> > +#define CHECK_PROT_ACCESS(prot, access_type) ((prot) & (1 << (access_type)))
>
> We don't want to use a macro when an inline function will work.

What's wrong with a macro? This has no local variables or any complex 
operation that would warant a function IMO it's just a conditional named 
for convenience so we don't have to type it everywhere and easier to see 
what is it for. A macro is just right for that.

> Does the compiler not see the pattern and transform the existing
> code into a shift? If it does then I would leave it. If not, then
> just keep prot_for_access_type but make it a shift and maybe
> comment the logic.

I don't know but prot_for_access_type is not even needed because this will 
work for that too passing PAGE_RWX for prot as done below at one place so 
no need for another function for that.

> I would call the new function check_prot_for_access_type().

I can rename it and could make it static inline but I like a macro for 
this better.

Regards,
BALATON Zoltan

> >  #ifndef CONFIG_USER_ONLY
> >
> > diff --git a/target/ppc/mmu-hash32.c b/target/ppc/mmu-hash32.c
> > index b5d7aeed4e..fa4a4ced6d 100644
> > --- a/target/ppc/mmu-hash32.c
> > +++ b/target/ppc/mmu-hash32.c
> > @@ -213,7 +213,7 @@ 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(*prot, access_type)) {
> >          *raddr = eaddr;
> >          return true;
> >      }
>
> This does read better, and better than the check_prot() below
> that it replaces too, so I like the cleanup.
>
> Thanks,
> Nick
>
> > @@ -364,7 +364,7 @@ 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(*protp, access_type)) {
> >                  if (guest_visible) {
> >                      if (access_type == MMU_INST_FETCH) {
> >                          cs->exception_index = POWERPC_EXCP_ISI;
> > @@ -432,7 +432,7 @@ 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(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 5a0d80feda..14c2116ae7 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(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..a72cd927c4 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(*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 eff015066d..24d68926b4 100644
> > --- a/target/ppc/mmu_common.c
> > +++ b/target/ppc/mmu_common.c
> > @@ -76,11 +76,6 @@ void ppc_store_sdr1(CPUPPCState *env, target_ulong value)
> >  /*****************************************************************************/
> >  /* PowerPC MMU emulation */
> >
> > -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)
> >  {
> > @@ -125,13 +120,14 @@ static int ppc6xx_tlb_pte_check(mmu_ctx_t *ctx, 
> > target_ulong pte0,
> >              /* Keep the matching PTE information */
> >              ctx->raddr = pte1;
> >              ctx->prot = ppc_hash32_pp_prot(ctx->key, pp, ctx->nx);
> > -            ret = check_prot(ctx->prot, access_type);
> > -            if (ret == 0) {
> > +            if (CHECK_PROT_ACCESS(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;
> >              }
> >          }
> >      }
> > @@ -317,12 +313,14 @@ 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(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;
> >              }
> > @@ -540,9 +538,11 @@ static int mmu40x_get_physical_address(CPUPPCState *env, 
> > mmu_ctx_t *ctx,
> >          check_perms:
> >              /* Check from TLB entry */
> >              ctx->prot = tlb->prot;
> > -            ret = check_prot(ctx->prot, access_type);
> > -            if (ret == -2) {
> > +            if (CHECK_PROT_ACCESS(ctx->prot, access_type)) {
> > +                ret = 0;
> > +            } else {
> >                  env->spr[SPR_40x_ESR] = 0;
> > +                ret = -2;
> >              }
> >              break;
> >          }
> > @@ -607,7 +607,7 @@ 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(*prot, access_type)) {
> >          qemu_log_mask(CPU_LOG_MMU, "%s: good TLB!\n", __func__);
> >          return 0;
> >      }
> > @@ -811,7 +811,7 @@ found_tlb:
> >              *prot |= PAGE_EXEC;
> >          }
> >      }
> > -    if (*prot & prot_for_access_type(access_type)) {
> > +    if (CHECK_PROT_ACCESS(*prot, access_type)) {
> >          qemu_log_mask(CPU_LOG_MMU, "%s: good TLB!\n", __func__);
> >          return 0;
> >      }