Re: [PATCH v5 08/14] KVM: s390: pv: handle secure storage exceptions for normal guests

[Janosch Frank]

On 10/12/21 10:35, Claudio Imbrenda wrote:
> On Tue, 12 Oct 2021 10:16:26 +0200
> Janosch Frank <frankja@xxxxxxxxxxxxx> wrote:
>
> > On 9/20/21 15:24, Claudio Imbrenda wrote:
> > > With upcoming patches, normal guests might touch secure pages.
> > >
> > > This patch extends the existing exception handler to convert the pages
> > > to non secure also when the exception is triggered by a normal guest.
> > >
> > > This can happen for example when a secure guest reboots; the first
> > > stage of a secure guest is non secure, and in general a secure guest
> > > can reboot into non-secure mode.
> > >
> > > If the secure memory of the previous boot has not been cleared up
> > > completely yet, a non-secure guest might touch secure memory, which
> > > will need to be handled properly.
> > >
> > > Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> > > ---
> > >    arch/s390/mm/fault.c | 10 +++++++++-
> > >    1 file changed, 9 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> > > index eb68b4f36927..74784581f42d 100644
> > > --- a/arch/s390/mm/fault.c
> > > +++ b/arch/s390/mm/fault.c
> > > @@ -767,6 +767,7 @@ void do_secure_storage_access(struct pt_regs *regs)
> > >    	struct vm_area_struct *vma;
> > >    	struct mm_struct *mm;
> > >    	struct page *page;
> > > +	struct gmap *gmap;
> > >    	int rc;
> > >    
> > >    	/*
> > > @@ -796,6 +797,14 @@ void do_secure_storage_access(struct pt_regs *regs)
> > >    	}
> > >    
> > >    	switch (get_fault_type(regs)) {
> > > +	case GMAP_FAULT:
> > > +		gmap = (struct gmap *)S390_lowcore.gmap;
> > > +		addr = __gmap_translate(gmap, addr);
> > > +		if (IS_ERR_VALUE(addr)) {
> > > +			do_fault_error(regs, VM_ACCESS_FLAGS, VM_FAULT_BADMAP);
> > > +			break;
> > > +		}
> > > +		fallthrough;
> >
> > This would trigger an export and not a destroy, right?
>
> correct. but this would only happen for leftover secure pages touched
> by non-secure guests, before the background thread could clean them up.

I.e. we don't expect to need the destroy speed boost?

> > >    	case USER_FAULT:
> > >    		mm = current->mm;
> > >    		mmap_read_lock(mm);
> > > @@ -824,7 +833,6 @@ void do_secure_storage_access(struct pt_regs *regs)
> > >    		if (rc)
> > >    			BUG();
> > >    		break;
> > > -	case GMAP_FAULT:
> > >    	default:
> > >    		do_fault_error(regs, VM_READ | VM_WRITE, VM_FAULT_BADMAP);
> > >    		WARN_ON_ONCE(1);
> > >