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SubjectRe: [PATCHv2 08/10] x86/mm: Replace compile-time checks for 5-level with runtime-time
On Tue, Aug 01, 2017 at 09:46:56AM +0200, Juergen Gross wrote:
> On 26/07/17 18:43, Kirill A. Shutemov wrote:
> > On Wed, Jul 26, 2017 at 09:28:16AM +0200, Juergen Gross wrote:
> >> On 25/07/17 11:05, Kirill A. Shutemov wrote:
> >>> On Tue, Jul 18, 2017 at 04:24:06PM +0200, Juergen Gross wrote:
> >>>> Xen PV guests will never run with 5-level-paging enabled. So I guess you
> >>>> can drop the complete if (IS_ENABLED(CONFIG_X86_5LEVEL)) {} block.
> >>>
> >>> There is more code to drop from mmu_pv.c.
> >>>
> >>> But while there, I thought if with boot-time 5-level paging switching we
> >>> can allow kernel to compile with XEN_PV and XEN_PVH, so the kernel image
> >>> can be used in these XEN modes with 4-level paging.
> >>>
> >>> Could you check if with the patch below we can boot in XEN_PV and XEN_PVH
> >>> modes?
> >>
> >> We can't. I have used your branch:
> >>
> >> git://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git
> >> la57/boot-switching/v2
> >>
> >> with this patch applied on top.
> >>
> >> Doesn't boot PV guest with X86_5LEVEL configured (very early crash).
> >
> > Hm. Okay.
> >
> > Have you tried PVH?
> >
> >> Doesn't build with X86_5LEVEL not configured:
> >>
> >> AS arch/x86/kernel/head_64.o
> >
> > I've fixed the patch and split the patch into two parts: cleanup and
> > re-enabling XEN_PV and XEN_PVH for X86_5LEVEL.
> >
> > There's chance that I screw somthing up in clenaup part. Could you check
> > that?
>
> Build is working with and without X86_5LEVEL configured.
>
> PV domU boots without X86_5LEVEL configured.
>
> PV domU crashes with X86_5LEVEL configured:
>
> xen_start_kernel()
> x86_64_start_reservations()
> start_kernel()
> setup_arch()
> early_ioremap_init()
> early_ioremap_pmd()
>
> In early_ioremap_pmd() there seems to be a call to p4d_val() which is an
> uninitialized paravirt operation in the Xen pv case.

Thanks for testing.

Could you check if patch below makes a difference?

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 8febaa318aa2..37e5ccc3890f 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -604,12 +604,12 @@ static inline p4dval_t p4d_val(p4d_t p4d)
return PVOP_CALLEE1(p4dval_t, pv_mmu_ops.p4d_val, p4d.p4d);
}

-static inline void set_pgd(pgd_t *pgdp, pgd_t pgd)
-{
- pgdval_t val = native_pgd_val(pgd);
-
- PVOP_VCALL2(pv_mmu_ops.set_pgd, pgdp, val);
-}
+#define set_pgd(pgdp, pgdval) do { \
+ if (p4d_folded) \
+ set_p4d((p4d_t *)(pgdp), (p4d_t) { (pgdval).pgd }); \
+ else \
+ PVOP_VCALL2(pv_mmu_ops.set_pgd, pgdp, native_pgd_val(pgdval)); \
+ } while (0)

#define pgd_clear(pgdp) do { \
if (!p4d_folded) \
@@ -834,6 +834,7 @@ static inline notrace unsigned long arch_local_irq_save(void)
}


+#if 0
/* Make sure as little as possible of this mess escapes. */
#undef PARAVIRT_CALL
#undef __PVOP_CALL
@@ -848,6 +849,7 @@ static inline notrace unsigned long arch_local_irq_save(void)
#undef PVOP_CALL3
#undef PVOP_VCALL4
#undef PVOP_CALL4
+#endif

extern void default_banner(void);

diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index 3116649302f2..ab1a4f0c65c5 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -558,6 +558,22 @@ static void xen_set_p4d(p4d_t *ptr, p4d_t val)

xen_mc_issue(PARAVIRT_LAZY_MMU);
}
+
+#if CONFIG_PGTABLE_LEVELS >= 5
+__visible p4dval_t xen_p4d_val(p4d_t p4d)
+{
+ return pte_mfn_to_pfn(p4d.p4d);
+}
+PV_CALLEE_SAVE_REGS_THUNK(xen_p4d_val);
+
+__visible p4d_t xen_make_p4d(p4dval_t p4d)
+{
+ p4d = pte_pfn_to_mfn(p4d);
+
+ return native_make_p4d(p4d);
+}
+PV_CALLEE_SAVE_REGS_THUNK(xen_make_p4d);
+#endif /* CONFIG_PGTABLE_LEVELS >= 5 */
#endif /* CONFIG_X86_64 */

static int xen_pmd_walk(struct mm_struct *mm, pmd_t *pmd,
@@ -2431,6 +2447,11 @@ static const struct pv_mmu_ops xen_mmu_ops __initconst = {

.alloc_pud = xen_alloc_pmd_init,
.release_pud = xen_release_pmd_init,
+
+#if CONFIG_PGTABLE_LEVELS >= 5
+ .p4d_val = PV_CALLEE_SAVE(xen_p4d_val),
+ .make_p4d = PV_CALLEE_SAVE(xen_make_p4d),
+#endif
#endif /* CONFIG_X86_64 */

.activate_mm = xen_activate_mm,
--
Kirill A. Shutemov
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