Subject: Re: [PATCH v8 2/8] kvmppc: Movement of pages between normal and secure memory

From: Bharata B Rao <[email-masked]>
Date: Wed, 18 Sep 2019 12:42:06 +0530

On Tue, Sep 17, 2019 at 04:31:39PM -0700, Sukadev Bhattiprolu wrote:
> 
> Minor: Can this allocation be outside the lock? I guess it would change
> the order of cleanup at the end of the function.

Cleanup has bitmap_clear which needs be under spinlock, so this order
of setup/alloc and cleanup will keep things simple is what I felt.

> 
> > +	spin_unlock(&kvmppc_uvmem_pfn_lock);
> > +
> > +	*rmap = uvmem_pfn | KVMPPC_RMAP_UVMEM_PFN;
> > +	pvt->rmap = rmap;
> > +	pvt->gpa = gpa;
> > +	pvt->lpid = lpid;
> > +	dpage->zone_device_data = pvt;
> > +
> > +	get_page(dpage);
> > +	return dpage;
> > +
> > +out_unlock:
> > +	unlock_page(dpage);
> > +out_clear:
> > +	bitmap_clear(kvmppc_uvmem_pfn_bitmap, uvmem_pfn - pfn_first, 1);
> 
> Reuse variable 'bit'  here?

Sure.

> 
> > +out:
> > +	spin_unlock(&kvmppc_uvmem_pfn_lock);
> > +	return NULL;
> > +}
> > +
> > +/*
> > + * Alloc a PFN from private device memory pool and copy page from normal
> > + * memory to secure memory using UV_PAGE_IN uvcall.
> > + */
> > +static int
> > +kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long start,
> > +		   unsigned long end, unsigned long *rmap,
> > +		   unsigned long gpa, unsigned int lpid,
> > +		   unsigned long page_shift)
> > +{
> > +	unsigned long src_pfn, dst_pfn = 0;
> > +	struct migrate_vma mig;
> > +	struct page *spage;
> > +	unsigned long pfn;
> > +	struct page *dpage;
> > +	int ret = 0;
> > +
> > +	memset(&mig, 0, sizeof(mig));
> > +	mig.vma = vma;
> > +	mig.start = start;
> > +	mig.end = end;
> > +	mig.src = &src_pfn;
> > +	mig.dst = &dst_pfn;
> > +
> > +	ret = migrate_vma_setup(&mig);
> > +	if (ret)
> > +		return ret;
> > +
> > +	spage = migrate_pfn_to_page(*mig.src);
> > +	pfn = *mig.src >> MIGRATE_PFN_SHIFT;
> > +	if (!spage || !(*mig.src & MIGRATE_PFN_MIGRATE)) {
> > +		ret = 0;
> 
> Do we want to return success here (and have caller return H_SUCCESS) if
> we can't find the source page?

spage is NULL for zero page. In this case we return success but there is
no UV_PAGE_IN involved.

Absence of MIGRATE_PFN_MIGRATE indicates that the requested page
can't be migrated. I haven't hit this case till now. Similar check
is also present in the nouveau driver. I am not sure if this is strictly
needed here.

Christoph, Jason - do you know if !(*mig.src & MIGRATE_PFN_MIGRATE)
check is required and if so in which cases will it be true?

> > + * Fault handler callback when HV touches any page that has been
> 
>  Nit: s/callback/callback. Called /

Yeah will rephrase.

Regards,
Bharata.