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
......@@ -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();
......
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