linux-kernel - [PATCH 1/5] x86, fpu: introduce fpu_load_guest

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251224001249.1041934-2-pbonzini@redhat.com>
Date: Wed, 24 Dec 2025 01:12:45 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: seanjc@...gle.com,
	x86@...nel.org,
	stable@...r.kernel.org
Subject: [PATCH 1/5] x86, fpu: introduce fpu_load_guest_fpstate()

Create a variant of fpregs_lock_and_load() that KVM can use in its
vCPU entry code after preemption has been disabled.  While basing
it on the existing logic in vcpu_enter_guest(), ensure that
fpregs_assert_state_consistent() always runs and sprinkle a few
more assertions.

Cc: stable@...r.kernel.org
Fixes: 820a6ee944e7 ("kvm: x86: Add emulation for IA32_XFD", 2022-01-14)
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/include/asm/fpu/api.h |  1 +
 arch/x86/kernel/fpu/core.c     | 17 +++++++++++++++++
 arch/x86/kvm/x86.c             |  8 +-------
 3 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index cd6f194a912b..0820b2621416 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -147,6 +147,7 @@ extern void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr);
 /* KVM specific functions */
 extern bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu);
 extern void fpu_free_guest_fpstate(struct fpu_guest *gfpu);
+extern void fpu_load_guest_fpstate(struct fpu_guest *gfpu);
 extern int fpu_swap_kvm_fpstate(struct fpu_guest *gfpu, bool enter_guest);
 extern int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64 xfeatures);
 
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 3ab27fb86618..a480fa8c65d5 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -878,6 +878,23 @@ void fpregs_lock_and_load(void)
 	fpregs_assert_state_consistent();
 }
 
+void fpu_load_guest_fpstate(struct fpu_guest *gfpu)
+{
+#ifdef CONFIG_X86_DEBUG_FPU
+	struct fpu *fpu = x86_task_fpu(current);
+	WARN_ON_ONCE(gfpu->fpstate != fpu->fpstate);
+#endif
+
+	lockdep_assert_preemption_disabled();
+	if (test_thread_flag(TIF_NEED_FPU_LOAD))
+		fpregs_restore_userregs();
+
+	fpregs_assert_state_consistent();
+	if (gfpu->xfd_err)
+		wrmsrq(MSR_IA32_XFD_ERR, gfpu->xfd_err);
+}
+EXPORT_SYMBOL_FOR_KVM(fpu_load_guest_fpstate);
+
 #ifdef CONFIG_X86_DEBUG_FPU
 /*
  * If current FPU state according to its tracking (loaded FPU context on this
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ff8812f3a129..01d95192dfc5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11300,13 +11300,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		kvm_make_request(KVM_REQ_EVENT, vcpu);
 	}
 
-	fpregs_assert_state_consistent();
-	if (test_thread_flag(TIF_NEED_FPU_LOAD))
-		switch_fpu_return();
-
-	if (vcpu->arch.guest_fpu.xfd_err)
-		wrmsrq(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
-
+	fpu_load_guest_fpstate(&vcpu->arch.guest_fpu);
 	kvm_load_xfeatures(vcpu, true);
 
 	if (unlikely(vcpu->arch.switch_db_regs &&
-- 
2.52.0