Re: [Xen-devel] [PATCH v2 2/2] x86/HVM: split page straddling emulated accesses in more cases

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.09.18 at 18:15, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: 03 September 2018 16:45
>>[...]
>> The extra call to known_glfn() from hvmemul_write() is just to preserve
>> original behavior; we should consider dropping this (also to make sure
>> the intended effect of 8cbd4fb0b7 ["x86/hvm: implement hvmemul_write()
>> using real mappings"] is achieved in all cases where it can be achieved
>> without further rework), or alternatively we perhaps ought to mirror
>> this in hvmemul_rmw().

If you really want me to do the change below, could I have an
opinion on the above as well, as this may imply further re-work
of the patch?

>> --- a/xen/arch/x86/hvm/emulate.c
>> +++ b/xen/arch/x86/hvm/emulate.c
>> @@ -1041,6 +1041,110 @@ static inline int hvmemul_linear_mmio_wr
>>                                        pfec, hvmemul_ctxt, translate);
>>  }
>> 
>> +static bool known_glfn(unsigned long addr, unsigned int bytes, uint32_t
>> pfec)
>> +{
>> +    const struct hvm_vcpu_io *vio = &current->arch.hvm.hvm_io;
>> +
>> +    if ( pfec & PFEC_write_access )
>> +    {
>> +        if ( !vio->mmio_access.write_access )
>> +            return false;
>> +    }
>> +    else if ( pfec & PFEC_insn_fetch )
>> +    {
>> +        if ( !vio->mmio_access.insn_fetch )
>> +            return false;
>> +    }
>> +    else if ( !vio->mmio_access.read_access )
>> +            return false;
>> +
>> +    return (vio->mmio_gla == (addr & PAGE_MASK) &&
>> +            (addr & ~PAGE_MASK) + bytes <= PAGE_SIZE);
>> +}
>> +
> 
> Would it be possible to split the introduction of the above function into a 
> separate patch? AFAICT it does not seem to be intrinsically involved with 
> handle page straddling. It was certainly not there in your RFC patch.

The need for (or at least desirability of) it became obvious with the addition
of the logic to the write and rmw paths. It _could_ be split out, but it now is
a strictly necessary part/prereq of the change here.

Jan



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel