Re: [PATCH V2 1/2] x86/efi: Unmap EFI boot services code/data regions from efi_pgd

Thomas Gleixner
2018-10-29T17:21:49Z

Sai,

On Mon, 29 Oct 2018, Thomas Gleixner wrote:
> On Fri, 26 Oct 2018, Sai Praneeth Prakhya wrote:
> >
> > +int kernel_unmap_pages_in_pgd(pgd_t *pgd, unsigned long address,
> > + unsigned long numpages)
> > +{
> > + int retval;
> > +
> > + /*
> > + * The typical sequence for unmapping is to find a pte through
> > + * lookup_address_in_pgd() (ideally, it should never return NULL because
> > + * the address is already mapped) and change it's protections.
> > + * As pfn is the *target* of a mapping, it's not useful while unmapping.
> > + */
> > + struct cpa_data cpa = {
> > + .vaddr = &address,
> > + .pgd = pgd,
> > + .numpages = numpages,
> > + .mask_set = __pgprot(0),
> > + .mask_clr = __pgprot(_PAGE_PRESENT | _PAGE_RW),
> > + .flags = 0,
> > + };
> > +
> > + retval = __change_page_attr_set_clr(&cpa, 0);
> > + __flush_tlb_all();
>
> So this looks like you copied it from kernel_map_pages_in_pgd() which has
> been discussed before to be not sufficient, but it can't be changed right
> now due to locking issues.

Managed to confuse myself. The place which cannot be changed is a different
one, but still for your call site __flush_tlb_all() might not be sufficient.

Thanks,

tglx