Hi Ingo, Thomas, below patch is an update to this series and I plan to include it in the next post. David H. Gutteridge (CC'ed) was so kind to do additional testing of these patches and found that a BUG_ON was triggered in vmalloc_sync_one() when PTI is enabled. My debugging showed that the bug was present before my patches but that they uncovered this bug by setting SHARED_KERNEL_PMD to 0 when PTI is enabled. So please have a look at the issue description below and the patch and let me know what you think. I know there are other and better variants to fix that, but I felt a rework to make the generic ioremap code more safe against this is out-of-scope at least for this patch-set. Thanks, Joerg >From 48cb37800794be8f0611e87f9ef23774c3b36ecc Mon Sep 17 00:00:00 2001 From: Joerg Roedel <joro@localhost.localdomain> Date: Wed, 11 Apr 2018 15:55:14 +0200 Subject: [PATCH] x86/pgtable: Don't set huge pud/pmd on non-leaf entries The pmd_set_huge() and pud_set_huge() functions are used from generic ioremap code to establish large mappings where this is possible. But the generic ioremap code does not check whether the pmd/pud entries are already populated with a non-leaf entry, so that any page-table pages these entries point to will be lost. Further, on x86-32 with SHARED_KERNEL_PMD=0, this causes a BUG_ON() in vmalloc_sync_one() when pmd entries are synced from swapper_pg_dir to the current page-table. This happens because the pmd entry from swapper_pg_dir was promoted to a huge-page entry while the current pgd still contains the non-leaf entry. Because both entries are present and point to a different page, the BUG_ON triggers. This was actually triggered with pti-x32 enabled in a KVM virtual machine by the graphics driver. A real and better fix for that would be to improve the page-table handling in the generic ioremap code. But that is out-of-scope for this patch-set and left for later work. Reported-by: David H. Gutteridge <dhgutteridge@xxxxxxxxxxxx> Signed-off-by: Joerg Roedel <jroedel@xxxxxxx> --- arch/x86/mm/pgtable.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index d95bc7b1ffb4..6b72d2805058 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -1,6 +1,7 @@ // SPDX-License-Identifier: GPL-2.0 #include <linux/mm.h> #include <linux/gfp.h> +#include <linux/hugetlb.h> #include <asm/pgalloc.h> #include <asm/pgtable.h> #include <asm/tlb.h> @@ -699,6 +700,10 @@ int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot) (mtrr != MTRR_TYPE_WRBACK)) return 0; + /* Bail out if we are we on a populated non-leaf entry */ + if (pud_present(*pud) && !pud_huge(*pud)) + return 0; + prot = pgprot_4k_2_large(prot); set_pte((pte_t *)pud, pfn_pte( @@ -727,6 +732,10 @@ int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot) return 0; } + /* Bail out if we are we on a populated non-leaf entry */ + if (pmd_present(*pmd) && !pmd_huge(*pmd)) + return 0; + prot = pgprot_4k_2_large(prot); set_pte((pte_t *)pmd, pfn_pte( -- 2.13.6
