On Thu, Sep 19, 2019 at 08:56:48PM +0200, gregkh@linuxfoundation.org wrote:

The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

Backport for 4.19.y below.

Will

--->8

From 58035bc4dbe01d110f03977c61e3c024e0cf33da Mon Sep 17 00:00:00 2001

From: Will Deacon will@kernel.org Date: Thu, 22 Aug 2019 14:58:37 +0100 Subject: [PATCH] Revert "arm64: Remove unnecessary ISBs from set_{pte,pmd,pud}"

commit d0b7a302d58abe24ed0f32a0672dd4c356bb73db upstream.

This reverts commit 24fe1b0efad4fcdd32ce46cffeab297f22581707.

Commit 24fe1b0efad4fcdd ("arm64: Remove unnecessary ISBs from set_{pte,pmd,pud}") removed ISB instructions immediately following updates to the page table, on the grounds that they are not required by the architecture and a DSB alone is sufficient to ensure that subsequent data accesses use the new translation:

DDI0487E_a, B2-128:

| ... no instruction that appears in program order after the DSB | instruction can alter any state of the system or perform any part of | its functionality until the DSB completes other than: | | * Being fetched from memory and decoded | * Reading the general-purpose, SIMD and floating-point, | Special-purpose, or System registers that are directly or indirectly | read without causing side-effects.

However, the same document also states the following:

DDI0487E_a, B2-125:

| DMB and DSB instructions affect reads and writes to the memory system | generated by Load/Store instructions and data or unified cache | maintenance instructions being executed by the PE. Instruction fetches | or accesses caused by a hardware translation table access are not | explicit accesses.

which appears to claim that the DSB alone is insufficient. Unfortunately, some CPU designers have followed the second clause above, whereas in Linux we've been relying on the first. This means that our mapping sequence:

MOV X0, <valid pte> STR X0, [Xptep] // Store new PTE to page table DSB ISHST LDR X1, [X2] // Translates using the new PTE

can actually raise a translation fault on the load instruction because the translation can be performed speculatively before the page table update and then marked as "faulting" by the CPU. For user PTEs, this is ok because we can handle the spurious fault, but for kernel PTEs and intermediate table entries this results in a panic().

Revert the offending commit to reintroduce the missing barriers.

Cc: stable@vger.kernel.org # 4.19.y only Fixes: 24fe1b0efad4fcdd ("arm64: Remove unnecessary ISBs from set_{pte,pmd,pud}") Reviewed-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Will Deacon will@kernel.org --- arch/arm64/include/asm/pgtable.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 2214a403f39b..212a48826655 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -224,8 +224,10 @@ static inline void set_pte(pte_t *ptep, pte_t pte) * Only if the new pte is valid and kernel, otherwise TLB maintenance * or update_mmu_cache() have the necessary barriers. */ - if (pte_valid_not_user(pte)) + if (pte_valid_not_user(pte)) { dsb(ishst); + isb(); + } }

extern void __sync_icache_dcache(pte_t pteval); @@ -432,6 +434,7 @@ static inline void set_pmd(pmd_t *pmdp, pmd_t pmd) { WRITE_ONCE(*pmdp, pmd); dsb(ishst); + isb(); }

static inline void pmd_clear(pmd_t *pmdp) @@ -483,6 +486,7 @@ static inline void set_pud(pud_t *pudp, pud_t pud) { WRITE_ONCE(*pudp, pud); dsb(ishst); + isb(); }

static inline void pud_clear(pud_t *pudp)