Re: [Qemu-devel] [PATCH 05/10] target-ppc: Use actual page size encodings from HPTE

[Alexander Graf <agraf@suse.de>]

On 01/25/2016 06:15 AM, David Gibson wrote:
> At present the 64-bit hash MMU code uses information from the SLB to
> determine the page size of a translation.  We do need that information to
> correctly look up the hash table.  However the MMU also allows a
> possibly larger page size to be encoded into the HPTE itself, which is used
> to populate the TLB.  At present qemu doesn't check that, and so doesn't
> support the MPSS "Multiple Page Size per Segment" feature.
>
> This makes a start on allowing this, by adding an hpte_page_shift()
> function which looks up the page size of an HPTE.  We use this to validate
> page sizes encodings on faults, and populate the qemu TLB with larger
> page sizes when appropriate.
>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>   target-ppc/mmu-hash64.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++---
>   1 file changed, 70 insertions(+), 4 deletions(-)
>
> diff --git a/target-ppc/mmu-hash64.c b/target-ppc/mmu-hash64.c
> index 28ad361..bcad826 100644
> --- a/target-ppc/mmu-hash64.c
> +++ b/target-ppc/mmu-hash64.c
> @@ -21,6 +21,7 @@
>   #include "exec/helper-proto.h"
>   #include "qemu/error-report.h"
>   #include "sysemu/kvm.h"
> +#include "qemu/error-report.h"
>   #include "kvm_ppc.h"
>   #include "mmu-hash64.h"
>   
> @@ -474,6 +475,43 @@ static hwaddr ppc_hash64_htab_lookup(PowerPCCPU *cpu,
>       return pte_offset;
>   }
>   
> +static unsigned hpte_page_shift(const struct ppc_one_seg_page_size *sps,
> +    uint64_t pte0, uint64_t pte1)
> +{
> +    int i;
> +
> +    if (!(pte0 & HPTE64_V_LARGE)) {
> +        if (sps->page_shift != 12) {
> +            /* 4kiB page in a non 4kiB segment */
> +            return 0;
> +        }
> +        /* Normal 4kiB page */
> +        return 12;
> +    }
> +
> +    for (i = 0; i < PPC_PAGE_SIZES_MAX_SZ; i++) {
> +        const struct ppc_one_page_size *ps = &sps->enc[i];
> +        uint64_t mask;
> +
> +        if (!ps->page_shift) {
> +            break;
> +        }
> +
> +        if (ps->page_shift == 12) {
> +            /* L bit is set so this can't be a 4kiB page */
> +            continue;
> +        }
> +
> +        mask = ((1ULL << ps->page_shift) - 1) & HPTE64_R_RPN;
> +
> +        if ((pte1 & mask) == ps->pte_enc) {
> +            return ps->page_shift;
> +        }
> +    }
> +
> +    return 0; /* Bad page size encoding */
> +}
> +
>   static hwaddr ppc_hash64_pte_raddr(unsigned page_shift, ppc_hash_pte64_t pte,
>                                      target_ulong eaddr)
>   {
> @@ -489,6 +527,7 @@ int ppc_hash64_handle_mmu_fault(PowerPCCPU *cpu, target_ulong eaddr,
>       CPUState *cs = CPU(cpu);
>       CPUPPCState *env = &cpu->env;
>       ppc_slb_t *slb;
> +    unsigned apshift;
>       hwaddr pte_offset;
>       ppc_hash_pte64_t pte;
>       int pp_prot, amr_prot, prot;
> @@ -552,6 +591,28 @@ int ppc_hash64_handle_mmu_fault(PowerPCCPU *cpu, target_ulong eaddr,
>       qemu_log_mask(CPU_LOG_MMU,
>                   "found PTE at offset %08" HWADDR_PRIx "\n", pte_offset);
>   
> +    /* Validate page size encoding */
> +    apshift = hpte_page_shift(slb->sps, pte.pte0, pte.pte1);
> +    if (!apshift) {
> +        error_report("Bad page size encoding in HPTE 0x%"PRIx64" - 0x%"PRIx64
> +                     " @ 0x%"HWADDR_PRIx, pte.pte0, pte.pte1, pte_offset);
> +        /* Treat it like a hash miss for the guest */
> +        if (rwx == 2) {
> +            cs->exception_index = POWERPC_EXCP_ISI;
> +            env->error_code = 0x40000000;
> +        } else {
> +            cs->exception_index = POWERPC_EXCP_DSI;
> +            env->error_code = 0;
> +            env->spr[SPR_DAR] = eaddr;
> +            if (rwx == 1) {
> +                env->spr[SPR_DSISR] = 0x42000000;
> +            } else {
> +                env->spr[SPR_DSISR] = 0x40000000;

I know that we don't do this for any other DSISR setting yet, but do you 
think we could mark the start here and use names for the bits instead? 
The kernel has a few nice defines.


Alex