Re: [PATCH v7] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests.

[Kalra, Ashish]

> On Dec 7, 2020, at 4:14 PM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> 
> On Mon, Dec 07, 2020 at 10:06:24PM +0000, Ashish Kalra wrote:
>> This is related to the earlier static adjustment of the SWIOTLB buffers
>> as per guest memory size and Konrad's feedback on the same, as copied
>> below : 
>> 
>>>> That is eating 128MB for 1GB, aka 12% of the guest memory allocated statically for this.
>>>> 
>>>> And for guests that are 2GB, that is 12% until it gets to 3GB when 
>>>> it is 8% and then 6% at 4GB.
>>>> 
>>>> I would prefer this to be based on your memory count, that is 6% of 
>>>> total memory.
> 
> So no rule of thumb and no measurements? Just a magic number 6.

It is more of an approximation of the earlier static adjustment which was 128M for <1G guests, 256M for 1G-4G guests and 512M for >4G guests.

Thanks,
Ashish