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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v1 06/13] xen/arm: Add ARCH_WORKAROUND_2 support for guests
On Tue, 5 Jun 2018, Julien Grall wrote:
> In order to offer ARCH_WORKAROUND_2 support to guests, we need to track the
> state of the workaround per-vCPU. The field 'pad' in cpu_info is now
> repurposed to store flags easily accessible in assembly.
>
> As the hypervisor will always run with the workaround enabled, we may
> need to enable (on guest exit) or disable (on guest entry) the
> workaround.
>
> A follow-up patch will add fastpath for the workaround for arm64 guests.
>
> Note that check_workaround_ssbd() is used instead of ssbd_get_state()
> because the former is implemented using an alternative. Thefore the code
> will be shortcut on affected platform.
>
> This is part of XSA-263.
>
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> ---
> Changes in v2:
> - Fix the condition in need_ssbd_flip()
> ---
> xen/arch/arm/domain.c | 8 ++++++++
> xen/arch/arm/traps.c | 20 ++++++++++++++++++++
> xen/arch/arm/vsmc.c | 37 +++++++++++++++++++++++++++++++++++++
> xen/include/asm-arm/current.h | 6 +++++-
> 4 files changed, 70 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> index 5a2a9a6b83..4baecc2447 100644
> --- a/xen/arch/arm/domain.c
> +++ b/xen/arch/arm/domain.c
> @@ -21,6 +21,7 @@
> #include <xen/wait.h>
>
> #include <asm/alternative.h>
> +#include <asm/cpuerrata.h>
> #include <asm/cpufeature.h>
> #include <asm/current.h>
> #include <asm/event.h>
> @@ -572,6 +573,13 @@ int vcpu_initialise(struct vcpu *v)
> if ( (rc = vcpu_vtimer_init(v)) != 0 )
> goto fail;
>
> + /*
> + * The workaround 2 (i.e SSBD mitigation) is enabled by default if
> + * supported.
> + */
> + if ( get_ssbd_state() == ARM_SSBD_RUNTIME )
> + v->arch.cpu_info->flags |= CPUINFO_WORKAROUND_2_FLAG;
> +
> return rc;
>
> fail:
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 5c18e918b0..315fc61f77 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -2011,10 +2011,23 @@ inject_abt:
> inject_iabt_exception(regs, gva, hsr.len);
> }
>
> +static inline bool needs_ssbd_flip(struct vcpu *v)
> +{
> + if ( !check_workaround_ssbd() )
> + return false;
> +
> + return !(v->arch.cpu_info->flags & CPUINFO_WORKAROUND_2_FLAG) &&
> + cpu_require_ssbd_mitigation();
> +}
> +
> static void enter_hypervisor_head(struct cpu_user_regs *regs)
> {
> if ( guest_mode(regs) )
> {
> + /* If the guest has disabled the workaround, bring it back on. */
> + if ( needs_ssbd_flip(current) )
> + arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_2_FID, 1, NULL);
> +
> /*
> * If we pended a virtual abort, preserve it until it gets cleared.
> * See ARM ARM DDI 0487A.j D1.14.3 (Virtual Interrupts) for details,
> @@ -2260,6 +2273,13 @@ void leave_hypervisor_tail(void)
> */
> SYNCHRONIZE_SERROR(SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT);
>
> + /*
> + * The hypervisor runs with the workaround always present.
> + * If the guest wants it disabled, so be it...
> + */
> + if ( needs_ssbd_flip(current) )
> + arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_2_FID, 0, NULL);
> +
> return;
> }
> local_irq_enable();
> diff --git a/xen/arch/arm/vsmc.c b/xen/arch/arm/vsmc.c
> index 40a80d5760..c4ccae6030 100644
> --- a/xen/arch/arm/vsmc.c
> +++ b/xen/arch/arm/vsmc.c
> @@ -18,6 +18,7 @@
> #include <xen/lib.h>
> #include <xen/types.h>
> #include <public/arch-arm/smccc.h>
> +#include <asm/cpuerrata.h>
> #include <asm/cpufeature.h>
> #include <asm/monitor.h>
> #include <asm/regs.h>
> @@ -104,6 +105,23 @@ static bool handle_arch(struct cpu_user_regs *regs)
> if ( cpus_have_cap(ARM_HARDEN_BRANCH_PREDICTOR) )
> ret = 0;
> break;
> + case ARM_SMCCC_ARCH_WORKAROUND_2_FID:
> + switch ( get_ssbd_state() )
> + {
> + case ARM_SSBD_UNKNOWN:
> + case ARM_SSBD_FORCE_DISABLE:
> + break;
> +
> + case ARM_SSBD_RUNTIME:
> + ret = ARM_SMCCC_SUCCESS;
> + break;
> +
> + case ARM_SSBD_FORCE_ENABLE:
> + case ARM_SSBD_MITIGATED:
> + ret = ARM_SMCCC_NOT_REQUIRED;
> + break;
> + }
> + break;
> }
>
> set_user_reg(regs, 0, ret);
> @@ -114,6 +132,25 @@ static bool handle_arch(struct cpu_user_regs *regs)
> case ARM_SMCCC_ARCH_WORKAROUND_1_FID:
> /* No return value */
> return true;
> +
> + case ARM_SMCCC_ARCH_WORKAROUND_2_FID:
> + {
> + bool enable = (uint32_t)get_user_reg(regs, 1);
> +
> + /*
> + * ARM_WORKAROUND_2_FID should only be called when mitigation
> + * state can be changed at runtime.
> + */
> + if ( unlikely(get_ssbd_state() != ARM_SSBD_RUNTIME) )
> + return true;
> +
> + if ( enable )
> + get_cpu_info()->flags |= CPUINFO_WORKAROUND_2_FLAG;
> + else
> + get_cpu_info()->flags &= ~CPUINFO_WORKAROUND_2_FLAG;
> +
> + return true;
> + }
> }
>
> return false;
> diff --git a/xen/include/asm-arm/current.h b/xen/include/asm-arm/current.h
> index 7a0971fdea..f9819b34fc 100644
> --- a/xen/include/asm-arm/current.h
> +++ b/xen/include/asm-arm/current.h
> @@ -7,6 +7,10 @@
> #include <asm/percpu.h>
> #include <asm/processor.h>
>
> +/* Tell whether the guest vCPU enabled Workaround 2 (i.e variant 4) */
> +#define CPUINFO_WORKAROUND_2_FLAG_SHIFT 0
> +#define CPUINFO_WORKAROUND_2_FLAG (_AC(1, U) <<
> CPUINFO_WORKAROUND_2_FLAG_SHIFT)
> +
> #ifndef __ASSEMBLY__
>
> struct vcpu;
> @@ -21,7 +25,7 @@ DECLARE_PER_CPU(struct vcpu *, curr_vcpu);
> struct cpu_info {
> struct cpu_user_regs guest_cpu_user_regs;
> unsigned long elr;
> - unsigned int pad;
> + uint32_t flags;
> };
>
> static inline struct cpu_info *get_cpu_info(void)
> --
> 2.11.0
>
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