Re: [PATCH v4 15/25] KVM: VMX: Extend VMX controls macro shenanigans

Nathan Chancellor
2022-07-22T21:04:43Z

On Fri, Jul 22, 2022 at 06:33:27PM +0000, Sean Christopherson wrote:
> On Thu, Jul 14, 2022, Vitaly Kuznetsov wrote:
> > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> > index 286c88e285ea..89eaab3495a6 100644
> > --- a/arch/x86/kvm/vmx/vmx.h
> > +++ b/arch/x86/kvm/vmx/vmx.h
> > @@ -467,6 +467,113 @@ static inline u8 vmx_get_rvi(void)
> > return vmcs_read16(GUEST_INTR_STATUS) & 0xff;
> > }
> >
> > +#define __KVM_REQ_VMX_VM_ENTRY_CONTROLS \
> > + (VM_ENTRY_LOAD_DEBUG_CONTROLS)
> > +#ifdef CONFIG_X86_64
> > + #define KVM_REQ_VMX_VM_ENTRY_CONTROLS \
> > + (__KVM_REQ_VMX_VM_ENTRY_CONTROLS | \
> > + VM_ENTRY_IA32E_MODE)
>
> This breaks 32-bit builds, but at least we know the assert works!
>
> vmx_set_efer() toggles VM_ENTRY_IA32E_MODE without a CONFIG_X86_64 guard. That
> should be easy enough to fix since KVM should never allow EFER_LMA. Compile
> tested patch at the bottom.
>
> More problematic is that clang-13 doesn't like the new asserts, and even worse gives
> a very cryptic error. I don't have bandwidth to look into this at the moment, and
> probably won't next week either.
>
> ERROR: modpost: "__compiletime_assert_533" [arch/x86/kvm/kvm-intel.ko] undefined!
> ERROR: modpost: "__compiletime_assert_531" [arch/x86/kvm/kvm-intel.ko] undefined!
> ERROR: modpost: "__compiletime_assert_532" [arch/x86/kvm/kvm-intel.ko] undefined!
> ERROR: modpost: "__compiletime_assert_530" [arch/x86/kvm/kvm-intel.ko] undefined!
> make[2]: *** [scripts/Makefile.modpost:128: modules-only.symvers] Error 1
> make[1]: *** [Makefile:1753: modules] Error 2
> make[1]: *** Waiting for unfinished jobs....

clang-14 added support for the error and warning attributes, which makes
the BUILD_BUG_ON failures look like GCC. With allmodconfig, this
becomes:

In file included from ../arch/x86/kvm/vmx/vmx.c:61:
In file included from ../arch/x86/kvm/vmx/nested.h:7:
../arch/x86/kvm/vmx/vmx.h:610:1: error: call to __compiletime_assert_1135 declared with 'error' attribute: BUILD_BUG_ON failed: !(val & (KVM_REQ_VMX_VM_ENTRY_CONTROLS | KVM_OPT_VMX_VM_ENTRY_CONTROLS))
BUILD_CONTROLS_SHADOW(vm_entry, VM_ENTRY_CONTROLS, 32)
^
../arch/x86/kvm/vmx/vmx.h:602:2: note: expanded from macro 'BUILD_CONTROLS_SHADOW'
BUILD_BUG_ON(!(val & (KVM_REQ_VMX_##uname | KVM_OPT_VMX_##uname))); \
^
../include/linux/build_bug.h:50:2: note: expanded from macro 'BUILD_BUG_ON'
BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
^
../include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
../include/linux/compiler_types.h:340:2: note: expanded from macro '_compiletime_assert'
__compiletime_assert(condition, msg, prefix, suffix)
^
../include/linux/compiler_types.h:333:4: note: expanded from macro '__compiletime_assert'
prefix ## suffix(); \
^
<scratch space>:259:1: note: expanded from here
__compiletime_assert_1135
^
In file included from ../arch/x86/kvm/vmx/vmx.c:61:
In file included from ../arch/x86/kvm/vmx/nested.h:7:
../arch/x86/kvm/vmx/vmx.h:610:1: error: call to __compiletime_assert_1136 declared with 'error' attribute: BUILD_BUG_ON failed: !(val & (KVM_REQ_VMX_VM_ENTRY_CONTROLS | KVM_OPT_VMX_VM_ENTRY_CONTROLS))
../arch/x86/kvm/vmx/vmx.h:607:2: note: expanded from macro 'BUILD_CONTROLS_SHADOW'
BUILD_BUG_ON(!(val & (KVM_REQ_VMX_##uname | KVM_OPT_VMX_##uname))); \
^
../include/linux/build_bug.h:50:2: note: expanded from macro 'BUILD_BUG_ON'
BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
^
../include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
../include/linux/compiler_types.h:340:2: note: expanded from macro '_compiletime_assert'
__compiletime_assert(condition, msg, prefix, suffix)
^
../include/linux/compiler_types.h:333:4: note: expanded from macro '__compiletime_assert'
prefix ## suffix(); \
^
<scratch space>:10:1: note: expanded from here
__compiletime_assert_1136
^
In file included from ../arch/x86/kvm/vmx/vmx.c:61:
In file included from ../arch/x86/kvm/vmx/nested.h:7:
../arch/x86/kvm/vmx/vmx.h:611:1: error: call to __compiletime_assert_1137 declared with 'error' attribute: BUILD_BUG_ON failed: !(val & (KVM_REQ_VMX_VM_EXIT_CONTROLS | KVM_OPT_VMX_VM_EXIT_CONTROLS))
BUILD_CONTROLS_SHADOW(vm_exit, VM_EXIT_CONTROLS, 32)
^
../arch/x86/kvm/vmx/vmx.h:602:2: note: expanded from macro 'BUILD_CONTROLS_SHADOW'
BUILD_BUG_ON(!(val & (KVM_REQ_VMX_##uname | KVM_OPT_VMX_##uname))); \
^
../include/linux/build_bug.h:50:2: note: expanded from macro 'BUILD_BUG_ON'
BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
^
../include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
../include/linux/compiler_types.h:340:2: note: expanded from macro '_compiletime_assert'
__compiletime_assert(condition, msg, prefix, suffix)
^
../include/linux/compiler_types.h:333:4: note: expanded from macro '__compiletime_assert'
prefix ## suffix(); \
^
<scratch space>:30:1: note: expanded from here
__compiletime_assert_1137
^
In file included from ../arch/x86/kvm/vmx/vmx.c:61:
In file included from ../arch/x86/kvm/vmx/nested.h:7:
../arch/x86/kvm/vmx/vmx.h:611:1: error: call to __compiletime_assert_1138 declared with 'error' attribute: BUILD_BUG_ON failed: !(val & (KVM_REQ_VMX_VM_EXIT_CONTROLS | KVM_OPT_VMX_VM_EXIT_CONTROLS))
../arch/x86/kvm/vmx/vmx.h:607:2: note: expanded from macro 'BUILD_CONTROLS_SHADOW'
BUILD_BUG_ON(!(val & (KVM_REQ_VMX_##uname | KVM_OPT_VMX_##uname))); \
^
../include/linux/build_bug.h:50:2: note: expanded from macro 'BUILD_BUG_ON'
BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
^
../include/linux/build_bug.h:39:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
#define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
^
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
../include/linux/compiler_types.h:340:2: note: expanded from macro '_compiletime_assert'
__compiletime_assert(condition, msg, prefix, suffix)
^
../include/linux/compiler_types.h:333:4: note: expanded from macro '__compiletime_assert'
prefix ## suffix(); \
^
<scratch space>:40:1: note: expanded from here
__compiletime_assert_1138
^
4 errors generated.

As you mentioned in the other comment on this patch, the 'inline'
keyword should be '__always_inline' in the BUILD_CONTROLS_SHADOW macro
and a couple of other functions need it for BUILD_BUG_ON to see the
value all the way through the call chain. The following diff resolves
those errors for me, hopefully it is useful!

Cheers,
Nathan

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 4ce7ed835e06..b97ed63ece56 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -790,7 +790,7 @@ static bool msr_write_intercepted(struct vcpu_vmx *vmx, u32 msr)
MSR_IA32_SPEC_CTRL);
}

-static void clear_atomic_switch_msr_special(struct vcpu_vmx *vmx,
+static __always_inline void clear_atomic_switch_msr_special(struct vcpu_vmx *vmx,
unsigned long entry, unsigned long exit)
{
vm_entry_controls_clearbit(vmx, entry);
@@ -848,7 +848,7 @@ static void clear_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr)
vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, m->host.nr);
}

-static void add_atomic_switch_msr_special(struct vcpu_vmx *vmx,
+static __always_inline void add_atomic_switch_msr_special(struct vcpu_vmx *vmx,
unsigned long entry, unsigned long exit,
unsigned long guest_val_vmcs, unsigned long host_val_vmcs,
u64 guest_val, u64 host_val)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 758f80c41beb..acefa5b5e1b9 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -597,12 +597,12 @@ static inline u##bits lname##_controls_get(struct vcpu_vmx *vmx) \
{ \
return __##lname##_controls_get(vmx->loaded_vmcs); \
} \
-static inline void lname##_controls_setbit(struct vcpu_vmx *vmx, u##bits val) \
+static __always_inline void lname##_controls_setbit(struct vcpu_vmx *vmx, u##bits val) \
{ \
BUILD_BUG_ON(!(val & (KVM_REQ_VMX_##uname | KVM_OPT_VMX_##uname))); \
lname##_controls_set(vmx, lname##_controls_get(vmx) | val); \
} \
-static inline void lname##_controls_clearbit(struct vcpu_vmx *vmx, u##bits val) \
+static __always_inline void lname##_controls_clearbit(struct vcpu_vmx *vmx, u##bits val) \
{ \
BUILD_BUG_ON(!(val & (KVM_REQ_VMX_##uname | KVM_OPT_VMX_##uname))); \
lname##_controls_set(vmx, lname##_controls_get(vmx) & ~val); \

> > +#else
> > + #define KVM_REQ_VMX_VM_ENTRY_CONTROLS \
> > + __KVM_REQ_VMX_VM_ENTRY_CONTROLS
> > +#endif
>
> EFER.LMA patch, compile tested only.
>
> ---
> From: Sean Christopherson <seanjc@google.com>
> Date: Fri, 22 Jul 2022 18:26:21 +0000
> Subject: [PATCH] KVM: VMX: Don't toggle VM_ENTRY_IA32E_MODE for 32-bit
> kernels/KVM
>
> Don't toggle VM_ENTRY_IA32E_MODE in 32-bit kernels/KVM and instead bug
> the VM if KVM attempts to run the guest with EFER.LMA=1. KVM doesn't
> support running 64-bit guests with 32-bit hosts.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/vmx/vmx.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index bff97babf381..8623607e596d 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -2894,10 +2894,15 @@ int vmx_set_efer(struct kvm_vcpu *vcpu, u64 efer)
> return 0;
>
> vcpu->arch.efer = efer;
> +#ifdef CONFIG_X86_64
> if (efer & EFER_LMA)
> vm_entry_controls_setbit(vmx, VM_ENTRY_IA32E_MODE);
> else
> vm_entry_controls_clearbit(vmx, VM_ENTRY_IA32E_MODE);
> +#else
> + if (KVM_BUG_ON(efer & EFER_LMA, vcpu->kvm))
> + return 1;
> +#endif
>
> vmx_setup_uret_msrs(vmx);
> return 0;
>
> base-commit: e22e2665637151a321433b2bb705f5c3b8da40bc
> --
>