Re: [Xen-devel] [PATCH 1/6] x86emul: generalize wbinvd() hook

[Jan Beulich <JBeulich@xxxxxxxx>]

On 02.07.2019 12:22, Paul Durrant wrote:
>> From: Jan Beulich <JBeulich@xxxxxxxx>
>> Sent: 01 July 2019 12:56
>>
>> @@ -2149,10 +2147,65 @@ static int hvmemul_write_msr(
>>        return rc;
>>    }
>>
>> -static int hvmemul_wbinvd(
>> +static int hvmemul_cache_op(
>> +    enum x86emul_cache_op op,
>> +    enum x86_segment seg,
>> +    unsigned long offset,
>>        struct x86_emulate_ctxt *ctxt)
>>    {
>> -    alternative_vcall(hvm_funcs.wbinvd_intercept);
>> +    struct hvm_emulate_ctxt *hvmemul_ctxt =
>> +        container_of(ctxt, struct hvm_emulate_ctxt, ctxt);
>> +    unsigned long addr, reps = 1;
>> +    uint32_t pfec = PFEC_page_present;
>> +    int rc;
>> +    void *mapping;
>> +
>> +    if ( !cache_flush_permitted(current->domain) )
>> +        return X86EMUL_OKAY;
>> +
>> +    switch ( op )
>> +    {
>> +    case x86emul_clflush:
>> +    case x86emul_clflushopt:
>> +    case x86emul_clwb:
>> +        ASSERT(!is_x86_system_segment(seg));
>> +
>> +        rc = hvmemul_virtual_to_linear(seg, offset, 0, &reps,
>> +                                       hvm_access_read, hvmemul_ctxt, 
>> &addr);
>> +        if ( rc != X86EMUL_OKAY )
>> +            break;
>> +
>> +        if ( hvmemul_ctxt->seg_reg[x86_seg_ss].dpl == 3 )
>> +            pfec |= PFEC_user_mode;
>> +
>> +        mapping = hvmemul_map_linear_addr(addr, 0, pfec, hvmemul_ctxt,
>> +                                          current->arch.hvm.data_cache);
>> +        if ( mapping == ERR_PTR(~X86EMUL_EXCEPTION) )
>> +            return X86EMUL_EXCEPTION;

This return ...

>> +        if ( IS_ERR_OR_NULL(mapping) )
>> +            break;
>> +
>> +        if ( cpu_has_clflush )
>> +        {
>> +            if ( op == x86emul_clwb && cpu_has_clwb )
>> +                clwb(mapping);
>> +            else if ( op == x86emul_clflushopt && cpu_has_clflushopt )
>> +                clflushopt(mapping);
>> +            else
>> +                clflush(mapping);
>> +
>> +            hvmemul_unmap_linear_addr(mapping, addr, 0, hvmemul_ctxt);
>> +            break;
>> +        }
>> +
>> +        hvmemul_unmap_linear_addr(mapping, addr, 0, hvmemul_ctxt);
> 
> Since the mapping is ditched here, why bother getting one at all in the
> !cpu_has_clflush case? Are you trying to flush out an error condition> that 
> was previously missed?

... is what I'm after: We want exception behavior to be correct.

Jan
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