On 21/05/18 12:45, Russell King wrote:
> We want SMCCC_ARCH_WORKAROUND_1 to be fast. As fast as possible.
> So let's intercept it as early as we can by testing for the
> function call number as soon as we've identified a HVC call
> coming from the guest.
>
> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
> ---
> arch/arm/kvm/hyp/hyp-entry.S | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/kvm/hyp/hyp-entry.S b/arch/arm/kvm/hyp/hyp-entry.S
> index 918a05dd2d63..67de45685e29 100644
> --- a/arch/arm/kvm/hyp/hyp-entry.S
> +++ b/arch/arm/kvm/hyp/hyp-entry.S
> @@ -16,6 +16,7 @@
> * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
> */
>
> +#include <linux/arm-smccc.h>
> #include <linux/linkage.h>
> #include <asm/kvm_arm.h>
> #include <asm/kvm_asm.h>
> @@ -202,7 +203,7 @@ ENDPROC(__hyp_do_panic)
> lsr r2, r2, #16
> and r2, r2, #0xff
> cmp r2, #0
> - bne guest_trap @ Guest called HVC
> + bne guest_hvc_trap @ Guest called HVC
>
> /*
> * Getting here means host called HVC, we shift parameters and branch
> @@ -253,6 +254,16 @@ THUMB( orr lr, #1)
> pop {r2, lr}
> eret
>
> +guest_hvc_trap:
> + movw ip, #:lower16:ARM_SMCCC_ARCH_WORKAROUND_1
> + movt ip, #:upper16:ARM_SMCCC_ARCH_WORKAROUND_1
r12 is a live guest register, and only r0-r2 are saved at that stage.
You could additionally corrupt r3 though, once you've identified that
you're in the context of an SMCCC 1.1 call.
You should be able to replace r12 with r2.
> + ldr r0, [sp] @ Guest's r0
> + teq r0, ip
> + bne guest_trap
> + pop {r0, r1, r2}
You could replace this slightly more efficient
add sp, sp, #12
since we don't need to restore those registers to the guest. r2 would be
left containing ARM_SMCCC_ARCH_WORKAROUND_1 (harmless), and r1 has the
HSR value (perfectly predictable).
> + mov r0, #0
> + eret
> +
> guest_trap:
> load_vcpu r0 @ Load VCPU pointer to r0
>
>
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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