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KVM: selftests: nVMX: Add enlightened MSR-Bitmap selftest

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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: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220203104620.277031-4-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov 2022-02-03 11:46:17 +01:00 committed by Paolo Bonzini
parent 761b5ebaa1
commit 70e477d996
1 changed files with 59 additions and 0 deletions
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59
tools/testing/selftests/kvm/x86_64/evmcs_test.c
View File

@ -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);