[bionic:linux-azure-4.15][PATCH 2/3] x86/process/64: Make save_fsgs_for_kvm() ready for FSGSBASE

[Marcelo Henrique Cerri]

From: Thomas Gleixner <tglx at linutronix.de>

BugLink: https://bugs.launchpad.net/bugs/1913294

save_fsgs_for_kvm() is invoked via

  vcpu_enter_guest()
    kvm_x86_ops.prepare_guest_switch(vcpu)
      vmx_prepare_switch_to_guest()
        save_fsgs_for_kvm()

with preemption disabled, but interrupts enabled.

The upcoming FSGSBASE based GS safe needs interrupts to be disabled. This
could be done in the helper function, but that function is also called from
switch_to() which has interrupts disabled already.

Disable interrupts inside save_fsgs_for_kvm() and rename the function to
current_save_fsgs() so it can be invoked from other places.

Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Sasha Levin <sashal at kernel.org>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Link: https://lkml.kernel.org/r/20200528201402.1708239-7-sashal@kernel.org
(backported from commit 6758034e4d6a7f0e26b748789ab1f83f3116d1b9)
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
---
 arch/x86/include/asm/processor.h |  4 +---
 arch/x86/kernel/process_64.c     | 15 +++++++++------
 arch/x86/kvm/vmx.c               |  2 +-
 3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 286bc96c67c8..c3a2392fa7ec 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -409,10 +409,8 @@ DECLARE_PER_CPU(char *, irq_stack_ptr);
 DECLARE_PER_CPU(unsigned int, irq_count);
 extern asmlinkage void ignore_sysret(void);
 
-#if IS_ENABLED(CONFIG_KVM)
 /* Save actual FS/GS selectors and bases to current->thread */
-void save_fsgs_for_kvm(void);
-#endif
+void current_save_fsgs(void);
 #else	/* X86_64 */
 #ifdef CONFIG_CC_STACKPROTECTOR
 /*
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index e976b6c1c26e..381c478184b1 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -218,18 +218,21 @@ static __always_inline void save_fsgs(struct task_struct *task)
 	}
 }
 
-#if IS_ENABLED(CONFIG_KVM)
 /*
  * While a process is running,current->thread.fsbase and current->thread.gsbase
- * may not match the corresponding CPU registers (see save_base_legacy()). KVM
- * wants an efficient way to save and restore FSBASE and GSBASE.
- * When FSGSBASE extensions are enabled, this will have to use RD{FS,GS}BASE.
+ * may not match the corresponding CPU registers (see save_base_legacy()).
  */
-void save_fsgs_for_kvm(void)
+void current_save_fsgs(void)
 {
+	unsigned long flags;
+
+	/* Interrupts need to be off for FSGSBASE */
+	local_irq_save(flags);
 	save_fsgs(current);
+	local_irq_restore(flags);
 }
-EXPORT_SYMBOL_GPL(save_fsgs_for_kvm);
+#if IS_ENABLED(CONFIG_KVM)
+EXPORT_SYMBOL_GPL(current_save_fsgs);
 #endif
 
 static __always_inline void loadseg(enum which_selector which,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index ca29acc1721f..79893adbcdac 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2324,7 +2324,7 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
 	vmx->host_state.gs_ldt_reload_needed = vmx->host_state.ldt_sel;
 
 #ifdef CONFIG_X86_64
-	save_fsgs_for_kvm();
+	current_save_fsgs();
 	vmx->host_state.fs_sel = current->thread.fsindex;
 	vmx->host_state.gs_sel = current->thread.gsindex;
 #else
-- 
2.25.1