Re: [PATCH v8 09/11] i386/pc: bounds check phys-bits against max used GPA

[Joao Martins]

On 7/18/22 14:56, Igor Mammedov wrote:
> On Mon, 18 Jul 2022 15:16:22 +0200
> Igor Mammedov <imammedo@redhat.com> wrote:
> 
>> On Fri, 15 Jul 2022 18:16:26 +0100
>> Joao Martins <joao.m.martins@oracle.com> wrote:
>>
>>> Calculate max *used* GPA against the CPU maximum possible address
>>> and error out if the former surprasses the latter. This ensures
>>> max used GPA is reacheable by configured phys-bits. Default phys-bits
>>> on Qemu is TCG_PHYS_ADDR_BITS (40) which is enough for the CPU to
>>> address 1Tb (0xff ffff ffff) or 1010G (0xfc ffff ffff) in AMD hosts
>>> with IOMMU.
>>>
>>> This is preparation for AMD guests with >1010G, where it will want relocate
>>> ram-above-4g to be after 1Tb instead of 4G.
>>>
>>> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>  
>>
>> Acked-by: Igor Mammedov <imammedo@redhat.com>
> [...]
> 
>>> +    return pc_pci_hole64_start() + pci_hole64_size - 1;
> 
> off by 1?
> 

If you add a size to a start of range, you get past the end, not
the actual end address. And given that we are supposed to return the
end address ... or am I seeing a non issue here?

[Also this was new in v8 predecessor patches didn't have it.]

>>> +}
>>> +
> [...]
>