Commit 70e477d9 authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Paolo Bonzini
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KVM: selftests: nVMX: Add enlightened MSR-Bitmap selftest 



Introduce a test for enlightened MSR-Bitmap feature (Hyper-V on KVM):
- Intercept access to MSR_FS_BASE in L1 and check that this works
 with enlightened MSR-Bitmap disabled.
- Enabled enlightened MSR-Bitmap and check that the intercept still works
as expected.
- Intercept access to MSR_GS_BASE but don't clear the corresponding bit
from 'hv_clean_fields', KVM is supposed to skip updating MSR-Bitmap02 and
thus the consequent access to the MSR from L2 will not get intercepted.
- Finally, clear the corresponding bit from 'hv_clean_fields' and check
that access to MSR_GS_BASE is now intercepted.

The test works with the assumption, that access to MSR_FS_BASE/MSR_GS_BASE
is not intercepted for L1. If this ever becomes not true the test will
fail as nested_vmx_exit_handled_msr() always checks L1's MSR-Bitmap for
L2 irrespective of 'hv_clean_fields'. The behavior is correct as
enlightened MSR-Bitmap feature is just an optimization, KVM is not obliged
to ignore updates when the corresponding bit in 'hv_clean_fields' stays
clear.

Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220203104620.277031-4-vkuznets@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 761b5eba

tools/testing/selftests/kvm/x86_64/evmcs_test.c

+59 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <stdlib.h>

#include <string.h>

#include <sys/ioctl.h>

#include <linux/bitmap.h>



#include "test_util.h"
@@ -32,6 +33,22 @@ static void guest_nmi_handler(struct ex_regs *regs) 
{

}



/* Exits to L1 destroy GRPs! */

static inline void rdmsr_fs_base(void)

{

	__asm__ __volatile__ ("mov $0xc0000100, %%rcx; rdmsr" : : :

			      "rax", "rbx", "rcx", "rdx",

			      "rsi", "rdi", "r8", "r9", "r10", "r11", "r12",

			      "r13", "r14", "r15");

}

static inline void rdmsr_gs_base(void)

{

	__asm__ __volatile__ ("mov $0xc0000101, %%rcx; rdmsr" : : :

			      "rax", "rbx", "rcx", "rdx",

			      "rsi", "rdi", "r8", "r9", "r10", "r11", "r12",

			      "r13", "r14", "r15");

}



void l2_guest_code(void)

{

	GUEST_SYNC(7);
@@ -41,6 +58,15 @@ void l2_guest_code(void) 
	/* Forced exit to L1 upon restore */

	GUEST_SYNC(9);



	vmcall();



	/* MSR-Bitmap tests */

	rdmsr_fs_base(); /* intercepted */

	rdmsr_fs_base(); /* intercepted */

	rdmsr_gs_base(); /* not intercepted */

	vmcall();

	rdmsr_gs_base(); /* intercepted */



	/* Done, exit to L1 and never come back.  */

	vmcall();

}
@@ -91,6 +117,39 @@ void guest_code(struct vmx_pages *vmx_pages) 


	GUEST_SYNC(10);



	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_VMCALL);

	current_evmcs->guest_rip += 3; /* vmcall */



	/* Intercept RDMSR 0xc0000100 */

	vmwrite(CPU_BASED_VM_EXEC_CONTROL, vmreadz(CPU_BASED_VM_EXEC_CONTROL) |

		CPU_BASED_USE_MSR_BITMAPS);

	set_bit(MSR_FS_BASE & 0x1fff, vmx_pages->msr + 0x400);

	GUEST_ASSERT(!vmresume());

	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_MSR_READ);

	current_evmcs->guest_rip += 2; /* rdmsr */



	/* Enable enlightened MSR bitmap */

	current_evmcs->hv_enlightenments_control.msr_bitmap = 1;

	GUEST_ASSERT(!vmresume());

	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_MSR_READ);

	current_evmcs->guest_rip += 2; /* rdmsr */



	/* Intercept RDMSR 0xc0000101 without telling KVM about it */

	set_bit(MSR_GS_BASE & 0x1fff, vmx_pages->msr + 0x400);

	/* Make sure HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP is set */

	current_evmcs->hv_clean_fields |= HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP;

	GUEST_ASSERT(!vmresume());

	/* Make sure we don't see EXIT_REASON_MSR_READ here so eMSR bitmap works */

	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_VMCALL);

	current_evmcs->guest_rip += 3; /* vmcall */



	/* Now tell KVM we've changed MSR-Bitmap */

	current_evmcs->hv_clean_fields &= ~HV_VMX_ENLIGHTENED_CLEAN_FIELD_MSR_BITMAP;

	GUEST_ASSERT(!vmresume());

	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_MSR_READ);

	current_evmcs->guest_rip += 2; /* rdmsr */



	GUEST_ASSERT(!vmresume());

	GUEST_ASSERT(vmreadz(VM_EXIT_REASON) == EXIT_REASON_VMCALL);

	GUEST_SYNC(11);