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authorDave Martin <Dave.Martin@arm.com>2017-10-31 15:51:16 +0000
committerWill Deacon <will.deacon@arm.com>2017-11-03 15:24:19 +0000
commit17eed27b02da88560b4592390952b9a71042ab8b (patch)
tree799f8a7588f674ec78cfa81d87e999fda5b9a162 /arch/arm64/kernel
parent4ffa09a939ab6d95655b3aee6ff79de48df95be7 (diff)
arm64/sve: KVM: Prevent guests from using SVE
Until KVM has full SVE support, guests must not be allowed to execute SVE instructions. This patch enables the necessary traps, and also ensures that the traps are disabled again on exit from the guest so that the host can still use SVE if it wants to. On guest exit, high bits of the SVE Zn registers may have been clobbered as a side-effect the execution of FPSIMD instructions in the guest. The existing KVM host FPSIMD restore code is not sufficient to restore these bits, so this patch explicitly marks the CPU as not containing cached vector state for any task, thus forcing a reload on the next return to userspace. This is an interim measure, in advance of adding full SVE awareness to KVM. This marking of cached vector state in the CPU as invalid is done using __this_cpu_write(fpsimd_last_state, NULL) in fpsimd.c. Due to the repeated use of this rather obscure operation, it makes sense to factor it out as a separate helper with a clearer name. This patch factors it out as fpsimd_flush_cpu_state(), and ports all callers to use it. As a side effect of this refactoring, a this_cpu_write() in fpsimd_cpu_pm_notifier() is changed to __this_cpu_write(). This should be fine, since cpu_pm_enter() is supposed to be called only with interrupts disabled. Signed-off-by: Dave Martin <Dave.Martin@arm.com> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Marc Zyngier <marc.zyngier@arm.com> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/kernel')
-rw-r--r--arch/arm64/kernel/fpsimd.c31
1 files changed, 29 insertions, 2 deletions
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 88e5e6aef300..931fd8dca91a 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1050,6 +1050,33 @@ void fpsimd_flush_task_state(struct task_struct *t)
t->thread.fpsimd_state.cpu = NR_CPUS;
}
+static inline void fpsimd_flush_cpu_state(void)
+{
+ __this_cpu_write(fpsimd_last_state, NULL);
+}
+
+/*
+ * Invalidate any task SVE state currently held in this CPU's regs.
+ *
+ * This is used to prevent the kernel from trying to reuse SVE register data
+ * that is detroyed by KVM guest enter/exit. This function should go away when
+ * KVM SVE support is implemented. Don't use it for anything else.
+ */
+#ifdef CONFIG_ARM64_SVE
+void sve_flush_cpu_state(void)
+{
+ struct fpsimd_state *const fpstate = __this_cpu_read(fpsimd_last_state);
+ struct task_struct *tsk;
+
+ if (!fpstate)
+ return;
+
+ tsk = container_of(fpstate, struct task_struct, thread.fpsimd_state);
+ if (test_tsk_thread_flag(tsk, TIF_SVE))
+ fpsimd_flush_cpu_state();
+}
+#endif /* CONFIG_ARM64_SVE */
+
#ifdef CONFIG_KERNEL_MODE_NEON
DEFINE_PER_CPU(bool, kernel_neon_busy);
@@ -1090,7 +1117,7 @@ void kernel_neon_begin(void)
}
/* Invalidate any task state remaining in the fpsimd regs: */
- __this_cpu_write(fpsimd_last_state, NULL);
+ fpsimd_flush_cpu_state();
preempt_disable();
@@ -1211,7 +1238,7 @@ static int fpsimd_cpu_pm_notifier(struct notifier_block *self,
case CPU_PM_ENTER:
if (current->mm)
task_fpsimd_save();
- this_cpu_write(fpsimd_last_state, NULL);
+ fpsimd_flush_cpu_state();
break;
case CPU_PM_EXIT:
if (current->mm)