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Message-ID: <20211022185312.954684740@linutronix.de>
Date: Fri, 22 Oct 2021 20:55:51 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: x86@...nel.org, "Liu, Jing2" <jing2.liu@...el.com>,
Paolo Bonzini <pbonzini@...hat.com>,
"Bae, Chang Seok" <chang.seok.bae@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Arjan van de Ven <arjan@...ux.intel.com>,
kvm@...r.kernel.org, "Nakajima, Jun" <jun.nakajima@...el.com>,
Sean Christopherson <seanjc@...gle.com>
Subject: [patch V2 2/4] x86/fpu: Provide infrastructure for KVM FPU cleanup
For the upcoming AMX support it's necessary to do a proper integration with
KVM. 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.
Provide:
- An allocator which initializes the state properly
- A replacement for the existing FPU swap mechanim
Aside of the reduced memory foot print, this also makes state switching
more efficient when TIF_FPU_NEED_LOAD is set. It does not require a memcpy
as the state is already correct in the to be swapped out fpstate.
The existing interfaces will be removed once KVM is converted over.
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
V2: Remove the restore_mask argument as the result is constant anyway - Paolo
---
arch/x86/include/asm/fpu/api.h | 13 ++++++
arch/x86/kernel/fpu/core.c | 85 ++++++++++++++++++++++++++++++++++++++---
2 files changed, 92 insertions(+), 6 deletions(-)
---
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -135,9 +135,22 @@ extern void fpu_init_fpstate_user(struct
extern void fpstate_clear_xstate_component(struct fpstate *fps, unsigned int xfeature);
/* KVM specific functions */
+extern bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu);
+extern void fpu_free_guest_fpstate(struct fpu_guest *gfpu);
+extern int fpu_swap_kvm_fpstate(struct fpu_guest *gfpu, bool enter_guest);
extern void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask);
extern int fpu_copy_kvm_uabi_to_fpstate(struct fpu *fpu, const void *buf, u64 xcr0, u32 *pkru);
extern void fpu_copy_fpstate_to_kvm_uabi(struct fpu *fpu, void *buf, unsigned int size, u32 pkru);
+static inline void fpstate_set_confidential(struct fpu_guest *gfpu)
+{
+ gfpu->fpstate->is_confidential = true;
+}
+
+static inline bool fpstate_is_confidential(struct fpu_guest *gfpu)
+{
+ return gfpu->fpstate->is_confidential;
+}
+
#endif /* _ASM_X86_FPU_API_H */
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -176,6 +176,75 @@ void fpu_reset_from_exception_fixup(void
}
#if IS_ENABLED(CONFIG_KVM)
+static void __fpstate_reset(struct fpstate *fpstate);
+
+bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
+{
+ struct fpstate *fpstate;
+ unsigned int size;
+
+ size = fpu_user_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
+ fpstate = vzalloc(size);
+ if (!fpstate)
+ return false;
+
+ __fpstate_reset(fpstate);
+ fpstate_init_user(fpstate);
+ fpstate->is_valloc = true;
+ fpstate->is_guest = true;
+
+ gfpu->fpstate = fpstate;
+ return true;
+}
+EXPORT_SYMBOL_GPL(fpu_alloc_guest_fpstate);
+
+void fpu_free_guest_fpstate(struct fpu_guest *gfpu)
+{
+ struct fpstate *fps = gfpu->fpstate;
+
+ if (!fps)
+ return;
+
+ if (WARN_ON_ONCE(!fps->is_valloc || !fps->is_guest || fps->in_use))
+ return;
+
+ gfpu->fpstate = NULL;
+ vfree(fps);
+}
+EXPORT_SYMBOL_GPL(fpu_free_guest_fpstate);
+
+int fpu_swap_kvm_fpstate(struct fpu_guest *guest_fpu, bool enter_guest)
+{
+ struct fpstate *guest_fps = guest_fpu->fpstate;
+ struct fpu *fpu = ¤t->thread.fpu;
+ struct fpstate *cur_fps = fpu->fpstate;
+
+ fpregs_lock();
+ if (!cur_fps->is_confidential && !test_thread_flag(TIF_NEED_FPU_LOAD))
+ save_fpregs_to_fpstate(fpu);
+
+ /* Swap fpstate */
+ if (enter_guest) {
+ fpu->__task_fpstate = cur_fps;
+ fpu->fpstate = guest_fps;
+ guest_fps->in_use = true;
+ } else {
+ guest_fps->in_use = false;
+ fpu->fpstate = fpu->__task_fpstate;
+ fpu->__task_fpstate = NULL;
+ }
+
+ cur_fps = fpu->fpstate;
+
+ if (!cur_fps->is_confidential)
+ restore_fpregs_from_fpstate(cur_fps, XFEATURE_MASK_FPSTATE);
+
+ fpregs_mark_activate();
+ fpregs_unlock();
+ return 0;
+}
+EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpstate);
+
void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask)
{
fpregs_lock();
@@ -352,16 +421,20 @@ void fpstate_init_user(struct fpstate *f
fpstate_init_fstate(fpstate);
}
+static void __fpstate_reset(struct fpstate *fpstate)
+{
+ /* Initialize sizes and feature masks */
+ fpstate->size = fpu_kernel_cfg.default_size;
+ fpstate->user_size = fpu_user_cfg.default_size;
+ fpstate->xfeatures = fpu_kernel_cfg.default_features;
+ fpstate->user_xfeatures = fpu_user_cfg.default_features;
+}
+
void fpstate_reset(struct fpu *fpu)
{
/* Set the fpstate pointer to the default fpstate */
fpu->fpstate = &fpu->__fpstate;
-
- /* Initialize sizes and feature masks */
- fpu->fpstate->size = fpu_kernel_cfg.default_size;
- fpu->fpstate->user_size = fpu_user_cfg.default_size;
- fpu->fpstate->xfeatures = fpu_kernel_cfg.default_features;
- fpu->fpstate->user_xfeatures = fpu_user_cfg.default_features;
+ __fpstate_reset(fpu->fpstate);
}
#if IS_ENABLED(CONFIG_KVM)
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