On 21/05/18 15:17, Dave Martin wrote:
> This patch adds SVE context saving to the hyp FPSIMD context switch
> path. This means that it is no longer necessary to save the host
> SVE state in advance of entering the guest, when in use.
>
> In order to avoid adding pointless complexity to the code, VHE is
> assumed if SVE is in use. VHE is an architectural prerequisite for
> SVE, so there is no good reason to turn CONFIG_ARM64_VHE off in
> kernels that support both SVE and KVM.
>
> Historically, software models exist that can expose the
> architecturally invalid configuration of SVE without VHE, so if
> this situation is detected at kvm_init() time then KVM will be
> disabled.
>
> Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx>
>
> ---
>
> * Stripped the following tags, reviewers please reconfirm:
>
> Formerly-Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxx>
> Formerly-Acked-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> Formerly-Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
>
> (Creation of a new file for this one change may be deemed undesirable,
> but there didn't seem to be a correct place to put it. There may also
> be a way around the circular include problem that I missed.)
>
> Changes since v8:
>
> * Add kvm_arch_check_supported() hook, and move arm64-specific check
> for SVE-implies-VHE into arch/arm64/.
>
> Due to circular header dependency problems, it is difficult to get
> the prototype for kvm_pr_*() functions in <asm/kvm_host.h>, so this
> patch puts arm64's kvm_arch_check_supported() hook out of line.
> This is not a hot function.
> ---
> arch/arm/include/asm/kvm_host.h | 1 +
> arch/arm64/Kconfig | 7 +++++++
> arch/arm64/include/asm/kvm_host.h | 1 +
> arch/arm64/kvm/Makefile | 2 +-
> arch/arm64/kvm/fpsimd.c | 1 -
> arch/arm64/kvm/hyp/switch.c | 20 +++++++++++++++++++-
> arch/arm64/kvm/init.c | 33 +++++++++++++++++++++++++++++++++
> virt/kvm/arm/arm.c | 6 ++++++
> 8 files changed, 68 insertions(+), 3 deletions(-)
> create mode 100644 arch/arm64/kvm/init.c
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index ac870b2..e627ef8 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -280,6 +280,7 @@ void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>
> struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
>
> +static inline int kvm_arch_check_supported(void) { return 0; }
> static inline void kvm_arch_hardware_unsetup(void) {}
> static inline void kvm_arch_sync_events(struct kvm *kvm) {}
> static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index eb2cf49..b0d3820 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1130,6 +1130,7 @@ endmenu
> config ARM64_SVE
> bool "ARM Scalable Vector Extension support"
> default y
> + depends on !KVM || ARM64_VHE
> help
> The Scalable Vector Extension (SVE) is an extension to the AArch64
> execution state which complements and extends the SIMD functionality
> @@ -1155,6 +1156,12 @@ config ARM64_SVE
> booting the kernel. If unsure and you are not observing these
> symptoms, you should assume that it is safe to say Y.
>
> + CPUs that support SVE are architecturally required to support the
> + Virtualization Host Extensions (VHE), so the kernel makes no
> + provision for supporting SVE alongside KVM without VHE enabled.
> + Thus, you will need to enable CONFIG_ARM64_VHE if you want to support
> + KVM in the same kernel image.
> +
> config ARM64_MODULE_PLTS
> bool
> select HAVE_MOD_ARCH_SPECIFIC
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index b3fe730..80f3985 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -405,6 +405,7 @@ static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
> kvm_call_hyp(__kvm_set_tpidr_el2, tpidr_el2);
> }
>
> +int kvm_arch_check_supported(void);
> static inline void kvm_arch_hardware_unsetup(void) {}
> static inline void kvm_arch_sync_events(struct kvm *kvm) {}
> static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
> diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
> index 0f2a135..5e66afe 100644
> --- a/arch/arm64/kvm/Makefile
> +++ b/arch/arm64/kvm/Makefile
> @@ -17,7 +17,7 @@ kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/arm.o $(KVM)/arm/mmu.o $(KVM)/arm/mmio.
> kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/psci.o $(KVM)/arm/perf.o
>
> kvm-$(CONFIG_KVM_ARM_HOST) += inject_fault.o regmap.o va_layout.o
> -kvm-$(CONFIG_KVM_ARM_HOST) += hyp.o hyp-init.o handle_exit.o
> +kvm-$(CONFIG_KVM_ARM_HOST) += init.o hyp.o hyp-init.o handle_exit.o
> kvm-$(CONFIG_KVM_ARM_HOST) += guest.o debug.o reset.o sys_regs.o sys_regs_generic_v8.o
> kvm-$(CONFIG_KVM_ARM_HOST) += vgic-sys-reg-v3.o fpsimd.o
> kvm-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/aarch32.o
> diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
> index d9b5f73..52185ec 100644
> --- a/arch/arm64/kvm/fpsimd.c
> +++ b/arch/arm64/kvm/fpsimd.c
> @@ -59,7 +59,6 @@ int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu)
> */
> void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
> {
> - BUG_ON(system_supports_sve());
> BUG_ON(!current->mm);
>
> vcpu->arch.flags &= ~(KVM_ARM64_FP_ENABLED | KVM_ARM64_HOST_SVE_IN_USE);
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 118f300..a6a8c7d 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -21,6 +21,7 @@
>
> #include <kvm/arm_psci.h>
>
> +#include <asm/cpufeature.h>
> #include <asm/kvm_asm.h>
> #include <asm/kvm_emulate.h>
> #include <asm/kvm_host.h>
> @@ -28,6 +29,7 @@
> #include <asm/kvm_mmu.h>
> #include <asm/fpsimd.h>
> #include <asm/debug-monitors.h>
> +#include <asm/processor.h>
> #include <asm/thread_info.h>
>
> /* Check whether the FP regs were dirtied while in the host-side run loop: */
> @@ -329,6 +331,8 @@ static bool __hyp_text __skip_instr(struct kvm_vcpu *vcpu)
> void __hyp_text __hyp_switch_fpsimd(u64 esr __always_unused,
> struct kvm_vcpu *vcpu)
> {
> + struct user_fpsimd_state *host_fpsimd = vcpu->arch.host_fpsimd_state;
> +
> if (has_vhe())
> write_sysreg(read_sysreg(cpacr_el1) | CPACR_EL1_FPEN,
> cpacr_el1);
> @@ -339,7 +343,21 @@ void __hyp_text __hyp_switch_fpsimd(u64 esr __always_unused,
> isb();
>
> if (vcpu->arch.flags & KVM_ARM64_FP_HOST) {
> - __fpsimd_save_state(vcpu->arch.host_fpsimd_state);
> + /*
> + * In the SVE case, VHE is assumed: it is enforced by
> + * Kconfig and kvm_arch_init().
> + */
> + if (system_supports_sve() &&
> + (vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE)) {
> + struct thread_struct *thread = container_of(
> + host_fpsimd,
> + struct thread_struct, uw.fpsimd_state);
> +
> + sve_save_state(sve_pffr(thread), &host_fpsimd->fpsr);
> + } else {
> + __fpsimd_save_state(host_fpsimd);
> + }
> +
> vcpu->arch.flags &= ~KVM_ARM64_FP_HOST;
> }
>
> diff --git a/arch/arm64/kvm/init.c b/arch/arm64/kvm/init.c
> new file mode 100644
> index 0000000..3b6e730
> --- /dev/null
> +++ b/arch/arm64/kvm/init.c
> @@ -0,0 +1,33 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * arch/arm64/kvm/init.c: KVM initialisation support
> + *
> + * Copyright 2018 Arm Limited
> + * Author: Dave Martin <Dave.Martin@xxxxxxx>
> + */
> +#include <linux/errno.h>
> +#include <linux/kvm_host.h>
> +#include <asm/cpufeature.h>
> +#include <asm/kvm_host.h>
> +
> +/* Additional arch-dependent checks for KVM usability */
> +int kvm_arch_check_supported(void)
> +{
> + /*
> + * VHE is a prerequisite for SVE in the Arm architecture, and
> + * Kconfig ensures that if system_supports_sve() here then
> + * CONFIG_ARM64_VHE is enabled, so if VHE support wasn't already
> + * detected and enabled, the CPU is architecturally
> + * noncompliant.
> + *
> + * Just in case this mismatch is seen, detect it, warn and give
> + * up. Supporting this forbidden configuration in Hyp would be
> + * pointless.
> + */
> + if (system_supports_sve() && !has_vhe()) {
> + kvm_pr_unimpl("SVE system without VHE unsupported. Broken cpu?");
> + return -ENODEV;
> + }
> +
> + return 0;
> +}
[entering bikeshedding territory]
I'm not exactly keen on this. This feels overkill, and a departure from
what we've been doing so far.
Why don't you simply have a helper in kvm_host.h that does:
static inline bool kvm_arm_check_sve_valid(void)
{
return !system_supports_sve() || has_vhe();
}
(and a canonical "return true;" implementation for 32bit)
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index bee226c..8518df0 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -16,6 +16,7 @@
> * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
> */
>
> +#include <linux/bug.h>
> #include <linux/cpu_pm.h>
> #include <linux/errno.h>
> #include <linux/err.h>
> @@ -41,6 +42,7 @@
> #include <asm/mman.h>
> #include <asm/tlbflush.h>
> #include <asm/cacheflush.h>
> +#include <asm/cpufeature.h>
> #include <asm/virt.h>
> #include <asm/kvm_arm.h>
> #include <asm/kvm_asm.h>
> @@ -1574,6 +1576,10 @@ int kvm_arch_init(void *opaque)
> return -ENODEV;
> }
>
> + err = kvm_arch_check_supported();
> + if (err)
> + return err;
> +
And turn this into:
if (!kvm_arm_check_sve_valid()) {
kvm_pr_unimpl("SVE system without VHE unsupported. Broken cpu?");
return -EINVAL;
}
It has the advantage of being obvious of what we check for, and doesn't
add any extra file.
Thoughts?
M.
--
Jazz is not dead. It just smells funny...
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