On 22/7/24 22:06, Jason Gunthorpe wrote:
On Mon, Jul 22, 2024 at 08:19:23PM +1000, Alexey Kardashevskiy wrote:
If there is vIOMMU, then the driver in the VM can decide whether it wants
private or shared memory for DMA, pass that new flag to dma_map() and 1)
have DMA memory allocated from the private pool (== no page state changes)
and 2) have C-bit set in the vIOMMU page table (which is in the VM memory).
Not all HW supports a flow like that.
Fair point but still, under what imaginary circumstance a driver could
decide to flip T=0/1 when up and running?
My V1 says "all IOVA below X are private and above - shared" (which is a hw
knob in absence of vIOMMU) and I set the X to all '1's just to mark it all
private.
Is that portable to other implementations?
Well, when used as a big knob - 0 or the max (== flip private/shared),
then yes :)
--
Alexey
