Dave Martin <Dave.Martin@xxxxxxx> writes:
> 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>
>
> ---
>
> * Tags stripped since v8, please reconfirm if possible:
>
> Formerly-Reviewed-by: Christoffer Dall <christoffer.dall at arm.com>
> Formerly-Acked-by: Marc Zyngier <marc.zyngier at arm.com>
> Formerly-Acked-by: Catalin Marinas <catalin.marinas at arm.com>
>
> Changes since v9:
>
> Requested by Marc Zyngier:
>
> * Inline check for VHE if SVE is present into kvm_host.h.
>
> The check has been renamed to the more specific
> kvm_arch_check_sve_has_vhe(), and the kvm_pr_unimpl() moved back to
> arm.c (to avoid circular include issues).
>
> arm.c is not single-arch code, but it is all Arm-specific, so
> adding a hook like this doesn't seem too unreasonable.
>
> 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 | 13 +++++++++++++
> arch/arm64/kvm/fpsimd.c | 1 -
> arch/arm64/kvm/hyp/switch.c | 20 +++++++++++++++++++-
> virt/kvm/arm/arm.c | 7 +++++++
> 6 files changed, 47 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index ac870b2..3b85bbb 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 bool kvm_arch_check_sve_has_vhe(void) { return true; }
> 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..06d5a61 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -405,6 +405,19 @@ static inline void __cpu_init_hyp_mode(phys_addr_t pgd_ptr,
> kvm_call_hyp(__kvm_set_tpidr_el2, tpidr_el2);
> }
>
> +static inline bool kvm_arch_check_sve_has_vhe(void)
> +{
> + /*
> + * The Arm architecture specifies that imlpementation of SVE
> + * requires VHE also to be implemented. The KVM code for arm64
> + * relies on this when SVE is present:
> + */
> + if (system_supports_sve())
> + return has_vhe();
> + else
> + return true;
> +}
> +
> 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/fpsimd.c b/arch/arm64/kvm/fpsimd.c
> index 365933a..dc6ecfa 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/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index bee226c..ce7c6f3 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 +1576,11 @@ int kvm_arch_init(void *opaque)
> return -ENODEV;
> }
>
> + if (!kvm_arch_check_sve_has_vhe()) {
> + kvm_pr_unimpl("SVE system without VHE unsupported. Broken cpu?");
> + return -ENODEV;
> + }
> +
Ahh this is going to be a pain when people want to enable system
emulation for SVE in QEMU given our patchy feature implementation (i.e.
we haven't done VHE yet). However that's totally our problem not yours
;-)
Reviewed-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
> for_each_online_cpu(cpu) {
> smp_call_function_single(cpu, check_kvm_target_cpu, &ret, 1);
> if (ret < 0) {
--
Alex Bennée
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