Re: [Xen-devel] [PATCH v4 06/12] xen/arm: compile and initialize vmap

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 29 Apr 2013, Ian Campbell wrote:
> On Sat, 2013-04-27 at 15:55 +0100, Stefano Stabellini wrote:
> > On Fri, 26 Apr 2013, Ian Campbell wrote:
> > > On Fri, 2013-04-26 at 16:28 +0100, Stefano Stabellini wrote:
> > > > Rename EARLY_VMAP_VIRT_END and EARLY_VMAP_VIRT_START to
> > > > VMAP_VIRT_END and VMAP_VIRT_START.
> > > > 
> > > > Defining VMAP_VIRT_START triggers the compilation of common/vmap.c.
> > > > 
> > > > Define PAGE_HYPERVISOR and MAP_SMALL_PAGES (unused on ARM, because we
> > > > only support 4K pages so as a matter of fact it is always set).
> > > > 
> > > > Implement map_pages_to_xen and destroy_xen_mappings.
> > > > 
> > > > Call vm_init from start_xen.
> > > > 
> > > > Changes in v4:
> > > > - remove flush_tlb_local() from create_xen_entries;
> > > 
> > > Do you think the related one in create_p2m can go too?
> > 
> > No, because the flush in create_p2m is the only flush present in that
> > function, and because we change p2m mappings there, we need to make sure
> > that the guest doesn't keep accessing the old ones.
> 
> Isn't that flush in the wrong place then, because a guest VCPU running
> on another PCPU could easily repopulate the TLB entry between that flush
> and the time we actually update the PTE.
> 
> At the point of the current flush should be not remember that a flush is
> required and do it at the end? Or clear+flush here and reinstate later.

I agree, I'll send a patch


> BTW, this flushes all VMIDs, in principal we need to only flush the
> guest's one, which requires this CPU to switch to that VMID, issue the
> (TLBIALL) and switch back to the callers VMID. An optimisation to keep
> in mind until later I think.
> 
> It appears to not be possible to flsh individual IPAs, so given a lack
> of insight into the guest VA->IPA mapping we cannot optimise beyond a
> full flush, shame!

right

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel