Re: [Xen-devel] [PATCH v1 1/4] kasan: introduce set_pmd_early_shadow()

[Jürgen Groß <jgross@xxxxxxxx>]

On 15.01.20 17:32, Sergey Dyasli wrote:
> On 15/01/2020 11:09, Jürgen Groß wrote:
> > On 15.01.20 11:54, Sergey Dyasli wrote:
> > > Hi Juergen,
> > >
> > > On 08/01/2020 15:20, Sergey Dyasli wrote:
> > > > It is incorrect to call pmd_populate_kernel() multiple times for the
> > > > same page table. Xen notices it during kasan_populate_early_shadow():
> > > >
> > > >       (XEN) mm.c:3222:d155v0 mfn 3704b already pinned
> > > >
> > > > This happens for kasan_early_shadow_pte when USE_SPLIT_PTE_PTLOCKS is
> > > > enabled. Fix this by introducing set_pmd_early_shadow() which calls
> > > > pmd_populate_kernel() only once and uses set_pmd() afterwards.
> > > >
> > > > Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
> > > Looks like the plan to use set_pmd() directly has failed: it's an
> > > arch-specific function and can't be used in arch-independent code
> > > (as kbuild test robot has proven).
> > >
> > > Do you see any way out of this other than disabling SPLIT_PTE_PTLOCKS
> > > for PV KASAN?
> > Change set_pmd_early_shadow() like the following:
> >
> > #ifdef CONFIG_XEN_PV
> > static inline void set_pmd_early_shadow(pmd_t *pmd, pte_t *early_shadow)
> > {
> >      static bool pmd_populated = false;
> >
> >      if (likely(pmd_populated)) {
> >          set_pmd(pmd, __pmd(__pa(early_shadow) | _PAGE_TABLE));
> >      } else {
> >          pmd_populate_kernel(&init_mm, pmd, early_shadow);
> >          pmd_populated = true;
> >      }
> > }
> > #else
> > static inline void set_pmd_early_shadow(pmd_t *pmd, pte_t *early_shadow)
> > {
> >      pmd_populate_kernel(&init_mm, pmd, early_shadow);
> > }
> > #endif
> >
> > ... and move it to include/xen/xen-ops.h and call it with
> > lm_alias(kasan_early_shadow_pte) as the second parameter.
> Your suggestion to use ifdef is really good, especially now when I
> figured out that CONFIG_XEN_PV implies X86. But I don't like the idea
> of kasan code calling a non-empty function from xen-ops.h when
> CONFIG_XEN_PV is not defined. I'd prefer to keep set_pmd_early_shadow()
> in mm/kasan/init.c with the suggested ifdef.
Fine with me.


Juergen

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel