KVM: arm64: Discard any SVE state when entering KVM guests

[ Upstream commit 93ae6b01bafee8fa385aa25ee7ebdb40057f6abe ]

Since 8383741ab2e773a99 (KVM: arm64: Get rid of host SVE tracking/saving)
KVM has not tracked the host SVE state, relying on the fact that we
currently disable SVE whenever we perform a syscall. This may not be true
in future since performance optimisation may result in us keeping SVE
enabled in order to avoid needing to take access traps to reenable it.
Handle this by clearing TIF_SVE and converting the stored task state to
FPSIMD format when preparing to run the guest.  This is done with a new
call fpsimd_kvm_prepare() to keep the direct state manipulation
functions internal to fpsimd.c.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221115094640.112848-2-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
[ Mark: trivial backport to v6.1 ]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/include/asm/fpsimd.h b/arch/arm64/include/asm/fpsimd.h
index 9a62884183e517b1d22ac9963badb2a8cc1ab346..f7faf0f4507c8dabcd397dde483fafd775f33c68 100644 (file)
--- a/arch/arm64/include/asm/fpsimd.h
+++ b/arch/arm64/include/asm/fpsimd.h
@@ -44,6 +44,7 @@ extern void fpsimd_signal_preserve_current_state(void);
 extern void fpsimd_preserve_current_state(void);
 extern void fpsimd_restore_current_state(void);
 extern void fpsimd_update_current_state(struct user_fpsimd_state const *state);
+extern void fpsimd_kvm_prepare(void);
 
 extern void fpsimd_bind_state_to_cpu(struct user_fpsimd_state *state,
                                     void *sve_state, unsigned int sve_vl);

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index e22571e57ae1ec74cc764817326d48bd8684edbd..57e89361edcb0454263ba0363b7f937477258f86 100644 (file)
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1108,6 +1108,29 @@ void fpsimd_signal_preserve_current_state(void)
                sve_to_fpsimd(current);
 }
 
+/*
+ * Called by KVM when entering the guest.
+ */
+void fpsimd_kvm_prepare(void)
+{
+       if (!system_supports_sve())
+               return;
+
+       /*
+        * KVM does not save host SVE state since we can only enter
+        * the guest from a syscall so the ABI means that only the
+        * non-saved SVE state needs to be saved.  If we have left
+        * SVE enabled for performance reasons then update the task
+        * state to be FPSIMD only.
+        */
+       get_cpu_fpsimd_context();
+
+       if (test_and_clear_thread_flag(TIF_SVE))
+               sve_to_fpsimd(current);
+
+       put_cpu_fpsimd_context();
+}
+
 /*
  * Associate current's FPSIMD context with this cpu
  * The caller must have ownership of the cpu FPSIMD context before calling

diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 24734bfcfaa00f3ace45dacfbc09cf6e91923821..16e29f03dcbf2e9736f45237470f59c6aa6a956b 100644 (file)
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -70,12 +70,14 @@ error:
 void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
 {
        BUG_ON(!current->mm);
-       BUG_ON(test_thread_flag(TIF_SVE));
 
        vcpu->arch.flags &= ~KVM_ARM64_FP_ENABLED;
        vcpu->arch.flags |= KVM_ARM64_FP_HOST;
 
+       fpsimd_kvm_prepare();
+
        vcpu->arch.flags &= ~KVM_ARM64_HOST_SVE_ENABLED;
+
        if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
                vcpu->arch.flags |= KVM_ARM64_HOST_SVE_ENABLED;
 }