Re: [PATCH] powerpc: Prepare to support kernel handling of IOMMUmap/unmap

[Alexey Kardashevskiy]

On 07/25/2013 08:26 PM, Alexey Kardashevskiy wrote:
> The current VFIO-on-POWER implementation supports only user mode
> driven mapping, i.e. QEMU is sending requests to map/unmap pages.
> However this approach is really slow, so we want to move that to KVM.
> Since H_PUT_TCE can be extremely performance sensitive (especially with
> network adapters where each packet needs to be mapped/unmapped) we chose
> to implement that as a "fast" hypercall directly in "real
> mode" (processor still in the guest context but MMU off).
> 
> To be able to do that, we need to provide some facilities to
> access the struct page count within that real mode environment as things
> like the sparsemem vmemmap mappings aren't accessible.
> 
> This adds an API to get page struct when MMU is off.
> 
> This adds to MM a new function put_page_unless_one() which drops a page
> if counter is bigger than 1. It is going to be used when MMU is off
> (real mode on PPC64 is the first user) and we want to make sure that page
> release will not happen in real mode as it may crash the kernel in
> a horrible way.


Yes, my english needs to be polished, I even know where :)


-- 
Alexey
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/