Re: [Xen-devel] [PATCH] x86/pvh: fix memory accounting for Dom0

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Sep 28, 2017 at 03:39:08PM +0000, Roger Pau Monné wrote:
> On Thu, Sep 28, 2017 at 01:18:55PM +0000, Jan Beulich wrote:
> > >>> On 28.09.17 at 12:16, <roger.pau@xxxxxxxxxx> wrote:
> > > Make sure that the memory for the paging structures in case of a HVM
> > > Dom0 is subtracted from the total amount of memory available for Dom0
> > > to use. Also take into account whether the IOMMU is sharing the
> > > page tables with HAP, or else also reserve some memory for the IOMMU
> > > page tables.
> > > 
> > > While there re-organize the code slightly so that the for loop and the
> > > need_paging local variable can be removed.
> > 
> > These two things very definitely should not be merged into a single
> > patch; I'm not convinced the reorg is correct in the first place. Note
> > how avail, which is being changed in the first iteration of the loop,
> > feeds back into the second iteration.
> 
> I'm afraid I don't understand why this is done. Also, the second loop
> is only going to happen when need_paging is true, which only happens
> for HVM guests using shadow or without shared pt with the IOMMU.

OK I think I'm starting to understand this. The need_paging thing it's
only done if the page tables are not shared because the iommu_enabled
has already reserved some memory for the page tables, that can be
shared with EPT. I think this is all very confusing, and the
calculations done for the iommu_enabled case are wrong. Xen should use
dom0_paging_pages instead.

I still don't understand the need for the 'for' loop.

Thanks, Roger.

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