On Thu, Sep 10, 2020 at 01:37:13PM +0100, Will Deacon wrote:
> On Wed, Sep 09, 2020 at 04:29:26PM +0100, Alexandru Elisei wrote:
> > On 9/7/20 4:23 PM, Will Deacon wrote:
> > > [..]
> > > +
> > > +int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
> > > + struct kvm_pgtable_walker *walker)
> > > +{
> > > + struct kvm_pgtable_walk_data walk_data = {
> > > + .pgt = pgt,
> > > + .addr = ALIGN_DOWN(addr, PAGE_SIZE),
> > > + .end = PAGE_ALIGN(walk_data.addr + size),
> > > + .walker = walker,
> > > + };
> >
> > If the caller wants to walk [0x500, 0x1500), for PAGE_SIZE = 0x1000 (4K), the
> > function walks the range [0x0, 0x1000). Is that intentional?
>
> Yes, although the caller specifies a base and a *size*, rather than an end
> address. As a concrete example, much of the hypervisor stage-1 mapping
> is created using PAGE_SIZE mappings of random ELF symbols, which correspond
> to arbitrary addresses. In these cases, we really do want to round-down the
> address and perform a PAGE_SIZE mapping.
I think Alexandru has a point here. Turning his example into something
equivalent that maps a random ELF symbol:
struct some_hyp_state s = { ... };
// &s == 0x500
// sizeof(s) == PAGE_SIZE
kvm_pgtable_walk(&s, sizeof(s), walker);
Given `s` straddles the two pages, the part in the second page won't be
mapped.
Should the end address instead be calculated as:
.end = PAGE_ALIGN(addr + size),
>
> The alternative would be to return an error if the size is not page-aligned,
> but I don't think that's really necessary, especially since we accept an
> unaligned base.
>
> Will
>
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