linux-kernel - RE: [RFC v1 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor.

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Message-Id: <20191106170153.GC5201@oc0525413822.ibm.com>
Date:   Wed, 6 Nov 2019 09:01:53 -0800
From:   Ram Pai <linuxram@...ibm.com>
To:     Alexey Kardashevskiy <aik@...abs.ru>
Cc:     linuxppc-dev@...ts.ozlabs.org, benh@...nel.crashing.org,
        david@...son.dropbear.id.au, mpe@...erman.id.au, paulus@...abs.org,
        mdroth@...ux.vnet.ibm.com, hch@....de, andmike@...ibm.com,
        sukadev@...ux.vnet.ibm.com, mst@...hat.com, ram.n.pai@...il.com,
        cai@....pw, tglx@...utronix.de, bauerman@...ux.ibm.com,
        linux-kernel@...r.kernel.org
Subject: RE: [RFC v1 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the
 hypervisor.

On Wed, Nov 06, 2019 at 12:58:50PM +1100, Alexey Kardashevskiy wrote:
> 
> 
> On 05/11/2019 08:28, Ram Pai wrote:
> > The hypervisor needs to access the contents of the page holding the TCE
> > entries while setting up the TCE entries in the IOMMU's TCE table. For
> > SecureVMs, since this page is encrypted, the hypervisor cannot access
> > valid entries. Share the page with the hypervisor. This ensures that the
> > hypervisor sees the valid entries.
> > 
> > Signed-off-by: Ram Pai <linuxram@...ibm.com>
> > ---
> >  arch/powerpc/platforms/pseries/iommu.c | 20 +++++++++++++++++---
> >  1 file changed, 17 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> > index 8d9c2b1..07f0847 100644
> > --- a/arch/powerpc/platforms/pseries/iommu.c
> > +++ b/arch/powerpc/platforms/pseries/iommu.c
> > @@ -37,6 +37,7 @@
> >  #include <asm/mmzone.h>
> >  #include <asm/plpar_wrappers.h>
> >  #include <asm/svm.h>
> > +#include <asm/ultravisor.h>
> >  
> >  #include "pseries.h"
> >  
> > @@ -179,6 +180,19 @@ static int tce_build_pSeriesLP(struct iommu_table *tbl, long tcenum,
> >  
> >  static DEFINE_PER_CPU(__be64 *, tce_page);
> >  
> > +/*
> > + * Allocate a tce page.  If secure VM, share the page with the hypervisor.
> > + */
> > +static __be64 *alloc_tce_page(void)
> > +{
> > +	__be64 *tcep = (__be64 *)__get_free_page(GFP_ATOMIC);
> > +
> > +	if (tcep && is_secure_guest())
> > +		uv_share_page(PHYS_PFN(__pa(tcep)), 1);
> 
> 
> There is no matching unshare in this patch.

The page is allocated and shared, and stays that way for the life of the
kernel. It is not explicitly unshared or freed.  It is however
implicitly unshared by the guest kernel, through a UV_UNSHARE_ALL_PAGES ucall
when the guest kernel reboots. And it also gets implicitly unshared by
the Ultravisor/Hypervisor, if the SVM abruptly terminates.

> 
> 
> > +
> > +	return tcep;
> > +}
> > +
> >  static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
> >  				     long npages, unsigned long uaddr,
> >  				     enum dma_data_direction direction,
> > @@ -206,8 +220,7 @@ static int tce_buildmulti_pSeriesLP(struct iommu_table *tbl, long tcenum,
> >  	 * from iommu_alloc{,_sg}()
> >  	 */
> >  	if (!tcep) {
> > -		tcep = (__be64 *)__get_free_page(GFP_ATOMIC);
> > -		/* If allocation fails, fall back to the loop implementation */
> > +		tcep = alloc_tce_page();
> >  		if (!tcep) {
> >  			local_irq_restore(flags);
> >  			return tce_build_pSeriesLP(tbl, tcenum, npages, uaddr,
> > @@ -391,6 +404,7 @@ static int tce_clearrange_multi_pSeriesLP(unsigned long start_pfn,
> >  	return rc;
> >  }
> >  
> > +
> 
> Unrelated.

yes. will fix it.

Thanks,
RP