@@ -127,6 +127,26 @@ static inline void cpu_install_idmap(void)
}
/*
+ * Atomically replaces the active TTBR1_EL1 PGD with a new VA-compatible PGD,
+ * avoiding the possibility of conflicting TLB entries being allocated.
+ */
+static inline void cpu_replace_ttbr1(pgd_t *pgd)
+{
+ typedef void (ttbr_replace_func)(phys_addr_t, phys_addr_t);
+ extern ttbr_replace_func idmap_cpu_replace_ttbr1;
+ ttbr_replace_func *replace_phys;
+
+ phys_addr_t pgd_phys = virt_to_phys(pgd);
+ phys_addr_t reserved_phys = virt_to_phys(empty_zero_page);
+
+ replace_phys = (void*)virt_to_phys(idmap_cpu_replace_ttbr1);
+
+ cpu_install_idmap();
+ replace_phys(pgd_phys, reserved_phys);
+ cpu_uninstall_idmap();
+}
+
+/*
* It would be nice to return ASIDs back to the allocator, but unfortunately
* that introduces a race with a generation rollover where we could erroneously
* free an ASID allocated in a future generation. We could workaround this by
@@ -139,6 +139,33 @@ ENTRY(cpu_do_switch_mm)
ret
ENDPROC(cpu_do_switch_mm)
+ .pushsection ".idmap.text", "ax"
+/*
+ * void idmap_cpu_replace_ttbr1(phys_addr_t new_pgd, phys_addr_t reserved_pgd)
+ *
+ * This is the low-level counterpart to cpu_replace_ttbr1, and should not be
+ * called by anything else. It can only be executed from a TTBR0 mapping.
+ */
+ENTRY(idmap_cpu_replace_ttbr1)
+ mrs x2, daif
+ msr daifset, #0xf
+
+ msr ttbr1_el1, x1
+ isb
+
+ tlbi vmalle1
+ dsb nsh
+ isb
+
+ msr ttbr1_el1, x0
+ isb
+
+ msr daif, x2
+
+ ret
+ENDPROC(idmap_cpu_replace_ttbr1)
+ .popsection
+
.section ".text.init", #alloc, #execinstr
/*
If page tables are modified without suitable TLB maintenance, the ARM architecture permits multiple TLB entries to be allocated for the same VA. When this occurs, it is permitted that TLB conflict aborts are raised in response to synchronous data/instruction accesses, and/or and amalgamation of the TLB entries may be used as a result of a TLB lookup. The presence of conflicting TLB entries may result in a variety of behaviours detrimental to the system (e.g. erroneous physical addresses may be used by I-cache fetches and/or page table walks). Some of these cases may result in unexpected changes of hardware state, and/or result in the (asynchronous) delivery of SError. To avoid these issues, we must avoid situations where conflicting entries may be allocated into TLBs. For user and module mappings we can follow a strict break-before-make approach, but this cannot work for modifications to the swapper page tables that cover the kernel text and data. Instead, this patch adds code which is intended to be executed from the idmap, which can safely unmap the swapper page tables as it only requires the idmap to be active. This enables us to uninstall the active TTBR1_EL1 entry, invalidate TLBs, then install a new TTBR1_EL1 entry without potentially unmapping code or data required for the sequence. This avoids the risk of conflict, but requires that updates are staged in a copy of the swapper page tables prior to being installed. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Jeremy Linton <jeremy.linton@arm.com> Cc: Laura Abbott <labbott@fedoraproject.org> Cc: Will Deacon <will.deacon@arm.com> --- arch/arm64/include/asm/mmu_context.h | 20 ++++++++++++++++++++ arch/arm64/mm/proc.S | 27 +++++++++++++++++++++++++++ 2 files changed, 47 insertions(+) -- 1.9.1 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel