[PATCH kernel v2 6/6] KVM: PPC: Add support for multiple-TCE hcalls

[Paul Mackerras]

On Fri, Feb 12, 2016 at 03:54:18PM +1100, Alexey Kardashevskiy wrote:
> On 02/11/2016 04:32 PM, Paul Mackerras wrote:
> >On Thu, Jan 21, 2016 at 06:39:37PM +1100, Alexey Kardashevskiy wrote:
> >>+	rmap = (void *) vmalloc_to_phys(rmap);
> >>+
> >>+	lock_rmap(rmap);
> >
> >A comment here explaining why we lock the rmap and what that achieves
> >would be useful for future generations.
> 
> 
> /* This protects the guest page with the TCE list from going away while we
> are reading TCE list */
> 
> ?
> 
> By "going away" I mean H_ENTER/H_REMOVE executed on parallel CPUs, is this
> roughly correct? as I did grep for "lock_rmap()" and did not find a single
> comment next to it...

Actually, taking the rmap lock stops the guest real -> host real
mapping from changing.  For the comment, I suggest this:

	/*
	 * Synchronize with the MMU notifier callbacks in
	 * book3s_64_mmu_hv.c (kvm_unmap_hva_hv etc.).
	 * While we have the rmap lock, code running on other CPUs
	 * cannot finish unmapping the host real page that backs
	 * this guest real page, so we are OK to access the host
	 * real page.
	 */

Paul.