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Subject[patch 2/6] x86/fpu: Prepare guest FPU for dynamically enabled FPU features
Date
To support dynamically enabled FPU features for guests prepare the guest
pseudo FPU container to keep track of the currently enabled xfeatures and
the guest permissions.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/include/asm/fpu/types.h | 13 +++++++++++++
arch/x86/kernel/fpu/core.c | 26 +++++++++++++++++++++++++-
2 files changed, 38 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -505,6 +505,19 @@ struct fpu {
*/
struct fpu_guest {
/*
+ * @xfeatures: xfeature bitmap of features which are
+ * currently enabled for the guest vCPU.
+ */
+ u64 xfeatures;
+
+ /*
+ * @perm: xfeature bitmap of features which are
+ * permitted to be enabled for the guest
+ * vCPU.
+ */
+ u64 perm;
+
+ /*
* @fpstate: Pointer to the allocated guest fpstate
*/
struct fpstate *fpstate;
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -201,6 +201,26 @@ void fpu_reset_from_exception_fixup(void
#if IS_ENABLED(CONFIG_KVM)
static void __fpstate_reset(struct fpstate *fpstate);

+static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
+{
+ struct fpu_state_perm *fpuperm;
+ u64 perm;
+
+ if (!IS_ENABLED(CONFIG_X86_64))
+ return;
+
+ spin_lock_irq(&current->sighand->siglock);
+ fpuperm = &current->group_leader->thread.fpu.guest_perm;
+ perm = fpuperm->__state_perm;
+
+ /* First fpstate allocation locks down permissions. */
+ WRITE_ONCE(fpuperm->__state_perm, perm | FPU_GUEST_PERM_LOCKED);
+
+ spin_unlock_irq(&current->sighand->siglock);
+
+ gfpu->perm = perm & ~FPU_GUEST_PERM_LOCKED;
+}
+
bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
{
struct fpstate *fpstate;
@@ -216,7 +236,11 @@ bool fpu_alloc_guest_fpstate(struct fpu_
fpstate->is_valloc = true;
fpstate->is_guest = true;

- gfpu->fpstate = fpstate;
+ gfpu->fpstate = fpstate;
+ gfpu->xfeatures = fpu_user_cfg.default_features;
+ gfpu->perm = fpu_user_cfg.default_features;
+ fpu_init_guest_permissions(gfpu);
+
return true;
}
EXPORT_SYMBOL_GPL(fpu_alloc_guest_fpstate);
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