On Wed, Jan 11, 2017 at 06:22:08PM +0000, Marc Zyngier wrote: > On 11/01/17 18:06, Catalin Marinas wrote: > > On Wed, Jan 11, 2017 at 09:41:15AM -0500, Christopher Covington wrote: > >> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S > >> index 32682be..9ee46df 100644 > >> --- a/arch/arm64/mm/proc.S > >> +++ b/arch/arm64/mm/proc.S > >> @@ -23,6 +23,7 @@ > >> #include <asm/assembler.h> > >> #include <asm/asm-offsets.h> > >> #include <asm/hwcap.h> > >> +#include <asm/mmu_context.h> > >> #include <asm/pgtable.h> > >> #include <asm/pgtable-hwdef.h> > >> #include <asm/cpufeature.h> > >> @@ -140,6 +141,18 @@ ENDPROC(cpu_do_resume) > >> ENTRY(cpu_do_switch_mm) > >> mmid x1, x1 // get mm->context.id > >> bfi x0, x1, #48, #16 // set the ASID > >> +#ifdef CONFIG_QCOM_FALKOR_ERRATUM_1003 > >> +alternative_if ARM64_WORKAROUND_QCOM_FALKOR_E1003 > >> + mrs x2, ttbr0_el1 > >> + mov x3, #FALKOR_RESERVED_ASID > >> + bfi x2, x3, #48, #16 // reserved ASID + old BADDR > >> + msr ttbr0_el1, x2 > >> + isb > >> + bfi x2, x0, #0, #48 // reserved ASID + new BADDR > >> + msr ttbr0_el1, x2 > >> + isb > >> +alternative_else_nop_endif > >> +#endif > >> msr ttbr0_el1, x0 // set TTBR0 > >> isb > >> post_ttbr0_update_workaround > > > > Please move the above hunk to a pre_ttbr0_update_workaround macro for > > consistency with post_ttbr0_update_workaround. > > In which case (and also for consistency), should we add that pre_ttbr0 > macro to entry.S, just before __uaccess_ttbr0_enable? It may not be > needed in the SW pan case, but it is probably worth entertaining the > idea that there may be something to do there... It may actually be needed in entry.S as well. With SW PAN, we move the context switching from cpu_do_switch_mm to the kernel_exit macro when returning to user. In this case we are switching from the reserved ASID 0 and reserved TTBR0_EL1 (pointing to a zeroed page) to the user's TTBR0_EL1 and ASID. If the ASID switch isn't taken into account, we may end up with new TLB entries being tagged with the reserved ASID. Apart from a potential loss of protection with TTBR0 PAN, is there anything else that could go wrong? Maybe a TLB conflict if we mix TLBs from multiple address spaces tagged with the same reserved ASID. If the above is an issue, we would need to patch __uaccess_ttbr0_enable() as well, though I'm more inclined to make this erratum not selectable when TTBR0 PAN is enabled. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
