lkml.org 
[lkml]   [2018]   [May]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 13/14] arm64: KVM: Handle guest's ARCH_WORKAROUND_2 requests
On Tue, May 22, 2018 at 04:06:47PM +0100, Marc Zyngier wrote:
> In order to forward the guest's ARCH_WORKAROUND_2 calls to EL3,
> add a small(-ish) sequence to handle it at EL2. Special care must
> be taken to track the state of the guest itself by updating the
> workaround flags. We also rely on patching to enable calls into
> the firmware.
>
> Note that since we need to execute branches, this always executes
> after the Spectre-v2 mitigation has been applied.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> arch/arm64/kernel/asm-offsets.c | 1 +
> arch/arm64/kvm/hyp/hyp-entry.S | 38 +++++++++++++++++++++++++++++++++++++-
> 2 files changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index 5bdda651bd05..323aeb5f2fe6 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -136,6 +136,7 @@ int main(void)
> #ifdef CONFIG_KVM_ARM_HOST
> DEFINE(VCPU_CONTEXT, offsetof(struct kvm_vcpu, arch.ctxt));
> DEFINE(VCPU_FAULT_DISR, offsetof(struct kvm_vcpu, arch.fault.disr_el1));
> + DEFINE(VCPU_WORKAROUND_FLAGS, offsetof(struct kvm_vcpu, arch.workaround_flags));
> DEFINE(CPU_GP_REGS, offsetof(struct kvm_cpu_context, gp_regs));
> DEFINE(CPU_USER_PT_REGS, offsetof(struct kvm_regs, regs));
> DEFINE(CPU_FP_REGS, offsetof(struct kvm_regs, fp_regs));
> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
> index bffece27b5c1..5b1fa37ca1f4 100644
> --- a/arch/arm64/kvm/hyp/hyp-entry.S
> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
> @@ -106,8 +106,44 @@ el1_hvc_guest:
> */
> ldr x1, [sp] // Guest's x0
> eor w1, w1, #ARM_SMCCC_ARCH_WORKAROUND_1
> + cbz w1, wa_epilogue
> +
> + /* ARM_SMCCC_ARCH_WORKAROUND_2 handling */
> + eor w1, w1, #(ARM_SMCCC_ARCH_WORKAROUND_1 ^ \
> + ARM_SMCCC_ARCH_WORKAROUND_2)

... that took me a second. Lovely. :)

> cbnz w1, el1_trap
> - mov x0, x1
> +
> +#ifdef CONFIG_ARM64_SSBD
> +alternative_cb arm64_enable_wa2_handling
> + b wa2_end
> +alternative_cb_end
> + get_vcpu_ptr x2, x0
> + ldr x0, [x2, #VCPU_WORKAROUND_FLAGS]
> +
> + /* Sanitize the argument and update the guest flags*/

Nit: space before the trailing '*/'. Either that or use a '//' comment.

Otherwise, this looks fine, so with that fixed:

Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> + ldr x1, [sp, #8] // Guest's x1
> + clz w1, w1 // Murphy's device:
> + lsr w1, w1, #5 // w1 = !!w1 without using
> + eor w1, w1, #1 // the flags...
> + bfi x0, x1, #VCPU_WORKAROUND_2_FLAG_SHIFT, #1
> + str x0, [x2, #VCPU_WORKAROUND_FLAGS]
> +
> + /* Check that we actually need to perform the call */
> + hyp_ldr_this_cpu x0, arm64_ssbd_callback_required, x2
> + cbz x0, wa2_end
> +
> + mov w0, #ARM_SMCCC_ARCH_WORKAROUND_2
> + smc #0
> +
> + /* Don't leak data from the SMC call */
> + mov x3, xzr
> +wa2_end:
> + mov x2, xzr
> + mov x1, xzr
> +#endif
> +
> +wa_epilogue:
> + mov x0, xzr
> add sp, sp, #16
> eret
>
> --
> 2.14.2
>

\
 
 \ /
  Last update: 2018-05-24 14:23    [W:0.207 / U:7.140 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site