On Mon, Jul 06, 2020 at 05:38:02PM +0100, Marc Zyngier wrote: > The current handling of erratum 1414080 has the side effect that > cntkctl_el1 can get changed for both 32 and 64bit tasks. > > This isn't a problem so far, but if we ever need to mitigate another > of these errata on the 64bit side, we'd better keep the messing with > cntkctl_el1 local to 32bit tasks. > > For that, make sure that on entering the kernel from a 32bit tasks, > userspace access to cntvct gets enabled, and disabled returning to > userspace, while it never gets changed for 64bit tasks. > > Signed-off-by: Marc Zyngier <[email protected]>
The asm looks sound to me. Suggestion below, but either way: Reviewed-by: Mark Rutland <[email protected]> > --- > arch/arm64/kernel/entry.S | 40 +++++++++++++++++++++++---------------- > 1 file changed, 24 insertions(+), 16 deletions(-) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 5304d193c79d..8f51f3273bc7 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -167,6 +167,19 @@ alternative_cb_end > stp x28, x29, [sp, #16 * 14] > > .if \el == 0 > + .if \regsize == 32 > + // If we come back from a 32bit task on a system affected by > + // 1418040, let's reenable userspace access to the virtual counter. > +#ifdef CONFIG_ARM64_ERRATUM_1418040 > +alternative_if_not ARM64_WORKAROUND_1418040 > + b .L__entry_skip_wa_1418040\@ > +alternative_else_nop_endif > + mrs x0, cntkctl_el1 > + orr x0, x0, #2 // ARCH_TIMER_USR_VCT_ACCESS_EN > + msr cntkctl_el1, x0 > +.L__entry_skip_wa_1418040\@: > +#endif Given this is only 3 instructions, it might be clearer to remove the branch and label and NOP the whole thing for legibility: | #ifdef CONFIG_ARM64_ERRATUM_1418040 | alternative_if ARM64_WORKAROUND_1418040 | mrs x0. cntkctl_el1 | orr x0, x0, #2 // ARCH_TIMER_USR_VCT_ACCESS_EN | msr cntkctl_el1, x0 | alternative_else_nop_endif | #endif ... and likewise for the clearing case. Regardless, this looks sound to me, so take your pick. :) Mark. > + .endif > clear_gp_regs > mrs x21, sp_el0 > ldr_this_cpu tsk, __entry_task, x20 > @@ -318,7 +331,17 @@ alternative_else_nop_endif > ldr x23, [sp, #S_SP] // load return stack pointer > msr sp_el0, x23 > tst x22, #PSR_MODE32_BIT // native task? > - b.eq 3f > + b.eq 4f > + > +#ifdef CONFIG_ARM64_ERRATUM_1418040 > +alternative_if_not ARM64_WORKAROUND_1418040 > + b 3f > +alternative_else_nop_endif > + mrs x1, cntkctl_el1 > + bic x1, x1, #2 // ARCH_TIMER_USR_VCT_ACCESS_EN > + msr cntkctl_el1, x1 > +3: > +#endif > > #ifdef CONFIG_ARM64_ERRATUM_845719 > alternative_if ARM64_WORKAROUND_845719 > @@ -330,22 +353,7 @@ alternative_if ARM64_WORKAROUND_845719 > #endif > alternative_else_nop_endif > #endif > -3: > -#ifdef CONFIG_ARM64_ERRATUM_1418040 > -alternative_if_not ARM64_WORKAROUND_1418040 > - b 4f > -alternative_else_nop_endif > - /* > - * if (x22.mode32 == cntkctl_el1.el0vcten) > - * cntkctl_el1.el0vcten = ~cntkctl_el1.el0vcten > - */ > - mrs x1, cntkctl_el1 > - eon x0, x1, x22, lsr #3 > - tbz x0, #1, 4f > - eor x1, x1, #2 // ARCH_TIMER_USR_VCT_ACCESS_EN > - msr cntkctl_el1, x1 > 4: > -#endif > scs_save tsk, x0 > > /* No kernel C function calls after this as user keys are set. */ > -- > 2.27.0 >
