Commit b2ac58f9 authored by KarimAllah Ahmed's avatar KarimAllah Ahmed Committed by Thomas Gleixner
Browse files

KVM/SVM: Allow direct access to MSR_IA32_SPEC_CTRL 



[ Based on a patch from Paolo Bonzini <pbonzini@redhat.com> ]

... basically doing exactly what we do for VMX:

- Passthrough SPEC_CTRL to guests (if enabled in guest CPUID)
- Save and restore SPEC_CTRL around VMExit and VMEntry only if the guest
  actually used it.

Signed-off-by: default avatarKarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarDarren Kenny <darren.kenny@oracle.com>
Reviewed-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jun Nakajima <jun.nakajima@intel.com>
Cc: kvm@vger.kernel.org
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Asit Mallick <asit.k.mallick@intel.com>
Cc: Arjan Van De Ven <arjan.van.de.ven@intel.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ashok Raj <ashok.raj@intel.com>
Link: https://lkml.kernel.org/r/1517669783-20732-1-git-send-email-karahmed@amazon.de
parent d28b387f

arch/x86/kvm/svm.c

+88 −0
Original line number Diff line number Diff line
@@ -184,6 +184,8 @@ struct vcpu_svm { 
		u64 gs_base;

	} host;



	u64 spec_ctrl;



	u32 *msrpm;



	ulong nmi_iret_rip;
@@ -249,6 +251,7 @@ static const struct svm_direct_access_msrs { 
	{ .index = MSR_CSTAR,				.always = true  },

	{ .index = MSR_SYSCALL_MASK,			.always = true  },

#endif

	{ .index = MSR_IA32_SPEC_CTRL,			.always = false },

	{ .index = MSR_IA32_PRED_CMD,			.always = false },

	{ .index = MSR_IA32_LASTBRANCHFROMIP,		.always = false },

	{ .index = MSR_IA32_LASTBRANCHTOIP,		.always = false },
@@ -882,6 +885,25 @@ static bool valid_msr_intercept(u32 index) 
	return false;

}



static bool msr_write_intercepted(struct kvm_vcpu *vcpu, unsigned msr)

{

	u8 bit_write;

	unsigned long tmp;

	u32 offset;

	u32 *msrpm;



	msrpm = is_guest_mode(vcpu) ? to_svm(vcpu)->nested.msrpm:

				      to_svm(vcpu)->msrpm;



	offset    = svm_msrpm_offset(msr);

	bit_write = 2 * (msr & 0x0f) + 1;

	tmp       = msrpm[offset];



	BUG_ON(offset == MSR_INVALID);



	return !!test_bit(bit_write,  &tmp);

}



static void set_msr_interception(u32 *msrpm, unsigned msr,

				 int read, int write)

{
@@ -1584,6 +1606,8 @@ static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) 
	u32 dummy;

	u32 eax = 1;



	svm->spec_ctrl = 0;



	if (!init_event) {

		svm->vcpu.arch.apic_base = APIC_DEFAULT_PHYS_BASE |

					   MSR_IA32_APICBASE_ENABLE;
@@ -3605,6 +3629,13 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) 
	case MSR_VM_CR:

		msr_info->data = svm->nested.vm_cr_msr;

		break;

	case MSR_IA32_SPEC_CTRL:

		if (!msr_info->host_initiated &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_IBRS))

			return 1;



		msr_info->data = svm->spec_ctrl;

		break;

	case MSR_IA32_UCODE_REV:

		msr_info->data = 0x01000065;

		break;
@@ -3696,6 +3727,33 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) 
	case MSR_IA32_TSC:

		kvm_write_tsc(vcpu, msr);

		break;

	case MSR_IA32_SPEC_CTRL:

		if (!msr->host_initiated &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_IBRS))

			return 1;



		/* The STIBP bit doesn't fault even if it's not advertised */

		if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP))

			return 1;



		svm->spec_ctrl = data;



		if (!data)

			break;



		/*

		 * For non-nested:

		 * When it's written (to non-zero) for the first time, pass

		 * it through.

		 *

		 * For nested:

		 * The handling of the MSR bitmap for L2 guests is done in

		 * nested_svm_vmrun_msrpm.

		 * We update the L1 MSR bit as well since it will end up

		 * touching the MSR anyway now.

		 */

		set_msr_interception(svm->msrpm, MSR_IA32_SPEC_CTRL, 1, 1);

		break;

	case MSR_IA32_PRED_CMD:

		if (!msr->host_initiated &&

		    !guest_cpuid_has(vcpu, X86_FEATURE_IBPB))
@@ -4964,6 +5022,15 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu) 


	local_irq_enable();



	/*

	 * If this vCPU has touched SPEC_CTRL, restore the guest's value if

	 * it's non-zero. Since vmentry is serialising on affected CPUs, there

	 * is no need to worry about the conditional branch over the wrmsr

	 * being speculatively taken.

	 */

	if (svm->spec_ctrl)

		wrmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);



	asm volatile (

		"push %%" _ASM_BP "; \n\t"

		"mov %c[rbx](%[svm]), %%" _ASM_BX " \n\t"
@@ -5056,6 +5123,27 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu) 
#endif

		);



	/*

	 * We do not use IBRS in the kernel. If this vCPU has used the

	 * SPEC_CTRL MSR it may have left it on; save the value and

	 * turn it off. This is much more efficient than blindly adding

	 * it to the atomic save/restore list. Especially as the former

	 * (Saving guest MSRs on vmexit) doesn't even exist in KVM.

	 *

	 * For non-nested case:

	 * If the L01 MSR bitmap does not intercept the MSR, then we need to

	 * save it.

	 *

	 * For nested case:

	 * If the L02 MSR bitmap does not intercept the MSR, then we need to

	 * save it.

	 */

	if (!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL))

		rdmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);



	if (svm->spec_ctrl)

		wrmsrl(MSR_IA32_SPEC_CTRL, 0);



	/* Eliminate branch target predictions from guest mode */

	vmexit_fill_RSB();

CRA Git | Maintained and supported by SUSTech CRA and CCSE