vmx_save_host_state() is only called from kvm_arch_vcpu_ioctl_run() so
the context is pretty well defined. Read MSR_{FS,KERNEL_GS}_BASE from
current->thread after calling save_fsgs() which takes care of
X86_BUG_NULL_SEG case now and will do RD[FG,GS]BASE when FSGSBASE
extensions are exposed to userspace (currently they are not).
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
arch/x86/include/asm/processor.h | 5 +++++
arch/x86/kernel/process_64.c | 14 ++++++++++++++
arch/x86/kvm/vmx.c | 13 ++++++++++---
3 files changed, 29 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index b0ccd4847a58..1d816a3325a1 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -410,6 +410,11 @@ DECLARE_INIT_PER_CPU(irq_stack_union);
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
#else /* X86_64 */
#ifdef CONFIG_CC_STACKPROTECTOR
/*
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 9eb448c7859d..4b100fe0f508 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -205,6 +205,20 @@ static __always_inline void save_fsgs(struct task_struct *task)
save_base_legacy(task, task->thread.gsindex, GS);
}
+#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.
+ */
+void save_fsgs_for_kvm(void)
+{
+ save_fsgs(current);
+}
+EXPORT_SYMBOL_GPL(save_fsgs_for_kvm);
+#endif
+
static __always_inline void loadseg(enum which_selector which,
unsigned short sel)
{
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 051dab74e4e9..189a347f3952 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2135,7 +2135,15 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
*/
vmx->host_state.ldt_sel = kvm_read_ldt();
vmx->host_state.gs_ldt_reload_needed = vmx->host_state.ldt_sel;
+
+#ifdef CONFIG_X86_64
+ save_fsgs_for_kvm();
+ vmx->host_state.fs_sel = current->thread.fsindex;
+ vmx->host_state.gs_sel = current->thread.gsindex;
+#else
savesegment(fs, vmx->host_state.fs_sel);
+ savesegment(gs, vmx->host_state.gs_sel);
+#endif
if (!(vmx->host_state.fs_sel & 7)) {
vmcs_write16(HOST_FS_SELECTOR, vmx->host_state.fs_sel);
vmx->host_state.fs_reload_needed = 0;
@@ -2143,7 +2151,6 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
vmcs_write16(HOST_FS_SELECTOR, 0);
vmx->host_state.fs_reload_needed = 1;
}
- savesegment(gs, vmx->host_state.gs_sel);
if (!(vmx->host_state.gs_sel & 7))
vmcs_write16(HOST_GS_SELECTOR, vmx->host_state.gs_sel);
else {
@@ -2157,7 +2164,7 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
#endif
#ifdef CONFIG_X86_64
- vmcs_writel(HOST_FS_BASE, read_msr(MSR_FS_BASE));
+ vmcs_writel(HOST_FS_BASE, current->thread.fsbase);
vmcs_writel(HOST_GS_BASE, read_msr(MSR_GS_BASE));
#else
vmcs_writel(HOST_FS_BASE, segment_base(vmx->host_state.fs_sel));
@@ -2165,7 +2172,7 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
#endif
#ifdef CONFIG_X86_64
- rdmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
+ vmx->msr_host_kernel_gs_base = current->thread.gsbase;
if (is_long_mode(&vmx->vcpu))
wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base);
#endif
--
2.14.3
