From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 22 Oct 2021 20:55:49 +0200
Subject: x86/fpu: Prepare for sanitizing KVM FPU code
Git-commit: 75c52dad5e327605f1025f399dafdf4aaf5dae9c
Patch-mainline: v5.15 or v5.15-rc8 (next release)
References: jsc#SLE-18931
For the upcoming AMX support it's necessary to do a proper integration with
KVM. To avoid more nasty hackery in KVM which violate encapsulation extend
struct fpu and fpstate so the fpstate switching can be consolidated and
simplified.
Currently KVM allocates two FPU structs which are used for saving the user
state of the vCPU thread and restoring the guest state when entering
vcpu_run() and doing the reverse operation before leaving vcpu_run().
With the new fpstate mechanism this can be reduced to one extra buffer by
swapping the fpstate pointer in current::thread::fpu. This makes the
upcoming support for AMX and XFD simpler because then fpstate information
(features, sizes, xfd) are always consistent and it does not require any
nasty workarounds.
Add fpu::__task_fpstate to save the regular fpstate pointer while the task
is inside vcpu_run(). Add some state fields to fpstate to indicate the
nature of the state.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211022185312.896403942@linutronix.de
---
arch/x86/include/asm/fpu/types.h | 44 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 43 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index a32be07f1418..c72cb2269adc 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -322,8 +322,32 @@ struct fpstate {
/* @user_xfeatures: xfeatures valid in UABI buffers */
u64 user_xfeatures;
+ /* @is_valloc: Indicator for dynamically allocated state */
+ unsigned int is_valloc : 1;
+
+ /* @is_guest: Indicator for guest state (KVM) */
+ unsigned int is_guest : 1;
+
+ /*
+ * @is_confidential: Indicator for KVM confidential mode.
+ * The FPU registers are restored by the
+ * vmentry firmware from encrypted guest
+ * memory. On vmexit the FPU registers are
+ * saved by firmware to encrypted guest memory
+ * and the registers are scrubbed before
+ * returning to the host. So there is no
+ * content which is worth saving and restoring.
+ * The fpstate has to be there so that
+ * preemption and softirq FPU usage works
+ * without special casing.
+ */
+ unsigned int is_confidential : 1;
+
+ /* @in_use: State is in use */
+ unsigned int in_use : 1;
+
/* @regs: The register state union for all supported formats */
- union fpregs_state regs;
+ union fpregs_state regs;
/* @regs is dynamically sized! Don't add anything after @regs! */
} __aligned(64);
@@ -363,6 +387,14 @@ struct fpu {
*/
struct fpstate *fpstate;
+ /*
+ * @__task_fpstate:
+ *
+ * Pointer to an inactive struct fpstate. Initialized to NULL. Is
+ * used only for KVM support to swap out the regular task fpstate.
+ */
+ struct fpstate *__task_fpstate;
+
/*
* @__fpstate:
*
@@ -378,6 +410,16 @@ struct fpu {
*/
};
+/*
+ * Guest pseudo FPU container
+ */
+struct fpu_guest {
+ /*
+ * @fpstate: Pointer to the allocated guest fpstate
+ */
+ struct fpstate *fpstate;
+};
+
/*
* FPU state configuration data. Initialized at boot time. Read only after init.
*/