Re: [Qemu-devel] [PATCH v5 2/3] softmmu: Add probe_write()

[Richard Henderson <rth@twiddle.net>]

On 05/26/2015 09:53 AM, Peter Maydell wrote:
> On 26 May 2015 at 17:49, Yongbok Kim <yongbok.kim@imgtec.com> wrote:
>> Add probe_write() forces a tlb_fill if the specified guest virtual
>> index isn't in the TCG softmmu TLB.
> 
> Surely the point is not to fill the TLB but to raise an
> exception if the address is not writable?
> 
>> +#if DATA_SIZE == 1
>> +/*
>> + * Force a tlb_fill if the specified guest virtual index isn't in the TCG
>> + * softmmu TLB.
>> + */
>> +void probe_write(CPUArchState *env, target_ulong addr, int mmu_idx,
>> +                 uintptr_t retaddr)
>> +{
>> +    int index = (addr >> TARGET_PAGE_BITS) & (CPU_TLB_SIZE - 1);
>> +    target_ulong tlb_addr = env->tlb_table[mmu_idx][index].addr_write;
>> +
>> +    if ((addr & TARGET_PAGE_MASK)
>> +        != (tlb_addr & (TARGET_PAGE_MASK | TLB_INVALID_MASK))) {
>> +        /* TLB entry is for a different page */
>> +        if (!VICTIM_TLB_HIT(addr_write)) {
>> +            tlb_fill(ENV_GET_CPU(env), addr, MMU_DATA_STORE, mmu_idx, retaddr);
>> +        }
>> +    }
>> +}
>> +#endif
>>  #endif /* !defined(SOFTMMU_CODE_ACCESS) */
> 
> I think this code does what you want, but the comments are
> rather misleading...

Indeed.  The fact that the TLB gets loaded is merely a happy side-effect.


r~