Re: [Qemu-devel] [PATCH v4 24/54] plugins: implement helpers for resolving hwaddr

[Richard Henderson]

On 8/1/19 7:14 AM, Aaron Lindsay OS via Qemu-devel wrote:
> On Jul 31 17:06, Alex Bennée wrote:
>> We need to keep a local per-cpu copy of the data as other threads may
>> be running. We use a automatically growing array and re-use the space
>> for subsequent queries.
> 
> [...]
> 
>> +bool tlb_plugin_lookup(CPUState *cpu, target_ulong addr, int mmu_idx,
>> +                       bool is_store, struct qemu_plugin_hwaddr *data)
>> +{
>> +    CPUArchState *env = cpu->env_ptr;
>> +    CPUTLBEntry *tlbe = tlb_entry(env, mmu_idx, addr);
>> +    target_ulong tlb_addr = is_store ? tlb_addr_write(tlbe) : 
>> tlbe->addr_read;
>> +
>> +    if (tlb_hit(tlb_addr, addr)) {
>> +        if (tlb_addr & TLB_MMIO) {
>> +            data->hostaddr = 0;
>> +            data->is_io = true;
>> +            /* XXX: lookup device */
>> +        } else {
>> +            data->hostaddr = addr + tlbe->addend;
>> +            data->is_io = false;
>> +        }
>> +        return true;
>> +    }
>> +    return false;
>> +}
> 
> In what cases do you expect tlb_hit() should not evaluate to true here?
> Will returns of false only be in error cases, or do you expect it can
> occur during normal operation? In particular, I'm interested in ensuring
> this is as reliable as possible, since some plugins may require physical
> addresses.

I have the same question.  Given the access has just succeeded, it would seem
to be that the tlb entry *must* hit.  No victim tlb check or anything.


r~