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KVM: VMX: Configure list of user return MSRs at module init

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Configure the list of user return MSRs that are actually supported at
module init instead of reprobing the list of possible MSRs every time a
vCPU is created.  Curating the list on a per-vCPU basis is pointless; KVM
is completely hosed if the set of supported MSRs changes after module init,
or if the set of MSRs differs per physical PCU.

The per-vCPU lists also increase complexity (see __vmx_find_uret_msr()) and
creates corner cases that _should_ be impossible, but theoretically exist
in KVM, e.g. advertising RDTSCP to userspace without actually being able to
virtualize RDTSCP if probing MSR_TSC_AUX fails.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210504171734.1434054-9-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-05-04 10:17:27 -07:00 committed by Paolo Bonzini
parent 36fa06f9ff
commit b6194b94a2
2 changed files with 50 additions and 21 deletions
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61
arch/x86/kvm/vmx/vmx.c
View File

@ -461,7 +461,7 @@ static unsigned long host_idt_base;
* support this emulation, IA32_STAR must always be included in
* vmx_uret_msrs_list[], even in i386 builds.
*/
static const u32 vmx_uret_msrs_list[] = {
static u32 vmx_uret_msrs_list[] = {
#ifdef CONFIG_X86_64
MSR_SYSCALL_MASK, MSR_LSTAR, MSR_CSTAR,
#endif
@ -469,6 +469,12 @@ static const u32 vmx_uret_msrs_list[] = {
MSR_IA32_TSX_CTRL,
};
/*
* Number of user return MSRs that are actually supported in hardware.
* vmx_uret_msrs_list is modified when KVM is loaded to drop unsupported MSRs.
*/
static int vmx_nr_uret_msrs;
#if IS_ENABLED(CONFIG_HYPERV)
static bool __read_mostly enlightened_vmcs = true;
module_param(enlightened_vmcs, bool, 0444);
@ -700,9 +706,16 @@ static inline int __vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr)
{
int i;
for (i = 0; i < vmx->nr_uret_msrs; ++i)
/*
* Note, vmx->guest_uret_msrs is the same size as vmx_uret_msrs_list,
* but is ordered differently. The MSR is matched against the list of
* supported uret MSRs using "slot", but the index that is returned is
* the index into guest_uret_msrs.
*/
for (i = 0; i < vmx_nr_uret_msrs; ++i) {
if (vmx_uret_msrs_list[vmx->guest_uret_msrs[i].slot] == msr)
return i;
}
return -1;
}
@ -6929,18 +6942,10 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
goto free_vpid;
}
BUILD_BUG_ON(ARRAY_SIZE(vmx_uret_msrs_list) != MAX_NR_USER_RETURN_MSRS);
for (i = 0; i < vmx_nr_uret_msrs; ++i) {
vmx->guest_uret_msrs[i].data = 0;
for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) {
u32 index = vmx_uret_msrs_list[i];
int j = vmx->nr_uret_msrs;
if (kvm_probe_user_return_msr(index))
continue;
vmx->guest_uret_msrs[j].slot = i;
vmx->guest_uret_msrs[j].data = 0;
switch (index) {
switch (vmx_uret_msrs_list[i]) {
case MSR_IA32_TSX_CTRL:
/*
* TSX_CTRL_CPUID_CLEAR is handled in the CPUID
@ -6954,15 +6959,14 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
* host so that TSX remains always disabled.
*/
if (boot_cpu_has(X86_FEATURE_RTM))
vmx->guest_uret_msrs[j].mask = ~(u64)TSX_CTRL_CPUID_CLEAR;
vmx->guest_uret_msrs[i].mask = ~(u64)TSX_CTRL_CPUID_CLEAR;
else
vmx->guest_uret_msrs[j].mask = 0;
vmx->guest_uret_msrs[i].mask = 0;
break;
default:
vmx->guest_uret_msrs[j].mask = -1ull;
vmx->guest_uret_msrs[i].mask = -1ull;
break;
}
++vmx->nr_uret_msrs;
}
err = alloc_loaded_vmcs(&vmx->vmcs01);
@ -7821,17 +7825,34 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
.vcpu_deliver_sipi_vector = kvm_vcpu_deliver_sipi_vector,
};
static __init void vmx_setup_user_return_msrs(void)
{
u32 msr;
int i;
BUILD_BUG_ON(ARRAY_SIZE(vmx_uret_msrs_list) != MAX_NR_USER_RETURN_MSRS);
for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i) {
msr = vmx_uret_msrs_list[i];
if (kvm_probe_user_return_msr(msr))
continue;
kvm_define_user_return_msr(vmx_nr_uret_msrs, msr);
vmx_uret_msrs_list[vmx_nr_uret_msrs++] = msr;
}
}
static __init int hardware_setup(void)
{
unsigned long host_bndcfgs;
struct desc_ptr dt;
int r, i, ept_lpage_level;
int r, ept_lpage_level;
store_idt(&dt);
host_idt_base = dt.address;
for (i = 0; i < ARRAY_SIZE(vmx_uret_msrs_list); ++i)
kvm_define_user_return_msr(i, vmx_uret_msrs_list[i]);
vmx_setup_user_return_msrs();
if (setup_vmcs_config(&vmcs_config, &vmx_capability) < 0)
return -EIO;

10
arch/x86/kvm/vmx/vmx.h
View File

@ -245,8 +245,16 @@ struct vcpu_vmx {
u32 idt_vectoring_info;
ulong rflags;
/*
* User return MSRs are always emulated when enabled in the guest, but
* only loaded into hardware when necessary, e.g. SYSCALL #UDs outside
* of 64-bit mode or if EFER.SCE=1, thus the SYSCALL MSRs don't need to
* be loaded into hardware if those conditions aren't met.
* nr_active_uret_msrs tracks the number of MSRs that need to be loaded
* into hardware when running the guest. guest_uret_msrs[] is resorted
* whenever the number of "active" uret MSRs is modified.
*/
struct vmx_uret_msr guest_uret_msrs[MAX_NR_USER_RETURN_MSRS];
int nr_uret_msrs;
int nr_active_uret_msrs;
bool guest_uret_msrs_loaded;
#ifdef CONFIG_X86_64