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Commit 42b933b5 authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Paolo Bonzini
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x86/kvm/vmx: read MSR_{FS,KERNEL_GS}_BASE from current->thread 



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).

Acked-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent b31c114b

arch/x86/include/asm/processor.h

+5 −0
Original line number Diff line number Diff line
@@ -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

/*

arch/x86/kernel/process_64.c

+14 −0
Original line number Diff line number Diff line
@@ -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)

{

arch/x86/kvm/vmx.c

+10 −3
Original line number Diff line number Diff line
@@ -2165,7 +2165,15 @@ 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;
@@ -2173,7 +2181,6 @@ 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 {
@@ -2187,7 +2194,7 @@ 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));
@@ -2195,7 +2202,7 @@ 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