work around gcc bugs with 'asm goto' with outputs

We've had issues with gcc and 'asm goto' before, and we created a
'asm_volatile_goto()' macro for that in the past: see commits
3f0116c3238a ("compiler/gcc4: Add quirk for 'asm goto' miscompilation
bug") and a9f180345f53 ("compiler/gcc4: Make quirk for
asm_volatile_goto() unconditional").

Then, much later, we ended up removing the workaround in commit
43c249ea0b1e ("compiler-gcc.h: remove ancient workaround for gcc PR
58670") because we no longer supported building the kernel with the
affected gcc versions, but we left the macro uses around.

Now, Sean Christopherson reports a new version of a very similar
problem, which is fixed by re-applying that ancient workaround. But the
problem in question is limited to only the 'asm goto with outputs'
cases, so instead of re-introducing the old workaround as-is, let's
rename and limit the workaround to just that much less common case.

It looks like there are at least two separate issues that all hit in
this area:

(a) some versions of gcc don't mark the asm goto as 'volatile' when it
has outputs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98619
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110420

which is easy to work around by just adding the 'volatile' by hand.

(b) Internal compiler errors:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110422

which are worked around by adding the extra empty 'asm' as a
barrier, as in the original workaround.

but the problem Sean sees may be a third thing since it involves bad
code generation (not an ICE) even with the manually added 'volatile'.

but the same old workaround works for this case, even if this feels a
bit like voodoo programming and may only be hiding the issue.

Reported-and-tested-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/all/20240208220604.140859-1-seanjc@google.com/
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Uros Bizjak <ubizjak@gmail.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: Andrew Pinski <quic_apinski@quicinc.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

KVM: VMX: Split off vmx_onhyperv.{ch} from hyperv.{ch}

hyperv.{ch} is currently a mix of stuff which is needed by both Hyper-V on
KVM and KVM on Hyper-V. As a preparation to making Hyper-V emulation
optional, put KVM-on-Hyper-V specific code into dedicated files.

No functional change intended.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Tested-by: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20231205103630.1391318-4-vkuznets@redhat.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: VMX: Use vmread_error() to report VM-Fail in "goto" path

Use vmread_error() to report VM-Fail on VMREAD for the "asm goto" case,
now that trampoline case has yet another wrapper around vmread_error() to
play nice with instrumentation.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230721235637.2345403-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: VMX: Make VMREAD error path play nice with noinstr

Mark vmread_error_trampoline() as noinstr, and add a second trampoline
for the CONFIG_CC_HAS_ASM_GOTO_OUTPUT=n case to enable instrumentation
when handling VM-Fail on VMREAD. VMREAD is used in various noinstr
flows, e.g. immediately after VM-Exit, and objtool rightly complains that
the call to the error trampoline leaves a no-instrumentation section
without annotating that it's safe to do so.

vmlinux.o: warning: objtool: vmx_vcpu_enter_exit+0xc9:
call to vmread_error_trampoline() leaves .noinstr.text section

Note, strictly speaking, enabling instrumentation in the VM-Fail path
isn't exactly safe, but if VMREAD fails the kernel/system is likely hosed
anyways, and logging that there is a fatal error is more important than
*maybe* encountering slightly unsafe instrumentation.

Reported-by: Su Hui <suhui@nfschina.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230721235637.2345403-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: VMX: Stub out enable_evmcs static key for CONFIG_HYPERV=n

Wrap enable_evmcs in a helper and stub it out when CONFIG_HYPERV=n in
order to eliminate the static branch nop placeholders. clang-14 is clever
enough to elide the nop, but gcc-12 is not. Stubbing out the key reduces
the size of kvm-intel.ko by ~7.5% (200KiB) when compiled with gcc-12
(there are a _lot_ of VMCS accesses throughout KVM).

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230211003534.564198-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: VMX: Allow VM-Fail path of VMREAD helper to be instrumented

Allow instrumentation in the VM-Fail path of __vmcs_readl() so that the
helper can be used in noinstr functions, e.g. to get the exit reason in
vmx_vcpu_enter_exit() in order to handle NMI VM-Exits in the noinstr
section. While allowing instrumentation isn't technically safe, KVM has
much bigger problems if VMREAD fails in a noinstr section.

Note, all other VMX instructions also allow instrumentation in their
VM-Fail paths for similar reasons, VMREAD was simply omitted by commit
3ebccdf373c2 ("x86/kvm/vmx: Move guest enter/exit into .noinstr.text")
because VMREAD wasn't used in a noinstr section at the time.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221213060912.654668-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

KVM: x86: Unify pr_fmt to use module name for all KVM modules

Define pr_fmt using KBUILD_MODNAME for all KVM x86 code so that printks
use consistent formatting across common x86, Intel, and AMD code. In
addition to providing consistent print formatting, using KBUILD_MODNAME,
e.g. kvm_amd and kvm_intel, allows referencing SVM and VMX (and SEV and
SGX and ...) as technologies without generating weird messages, and
without causing naming conflicts with other kernel code, e.g. "SEV: ",
"tdx: ", "sgx: " etc.. are all used by the kernel for non-KVM subsystems.

Opportunistically move away from printk() for prints that need to be
modified anyways, e.g. to drop a manual "kvm: " prefix.

Opportunistically convert a few SGX WARNs that are similarly modified to
WARN_ONCE; in the very unlikely event that the WARNs fire, odds are good
that they would fire repeatedly and spam the kernel log without providing
unique information in each print.

Note, defining pr_fmt yields undesirable results for code that uses KVM's
printk wrappers, e.g. vcpu_unimpl(). But, that's a pre-existing problem
as SVM/kvm_amd already defines a pr_fmt, and thankfully use of KVM's
wrappers is relatively limited in KVM x86 code.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Message-Id: <20221130230934.1014142-35-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: VMX: Make vmread_error_trampoline() uncallable from C code

Declare vmread_error_trampoline() as an opaque symbol so that it cannot
be called from C code, at least not without some serious fudging. The
trampoline always passes parameters on the stack so that the inline
VMREAD sequence doesn't need to clobber registers. regparm(0) was
originally added to document the stack behavior, but it ended up being
confusing because regparm(0) is a nop for 64-bit targets.

Opportunustically wrap the trampoline and its declaration in #ifdeffery
to make it even harder to invoke incorrectly, to document why it exists,
and so that it's not left behind if/when CONFIG_CC_HAS_ASM_GOTO_OUTPUT
is true for all supported toolchains.

No functional change intended.

Cc: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220928232015.745948-1-seanjc@google.com

KVM: VMX: Rename "vmx/evmcs.{ch}" to "vmx/hyperv.{ch}"

To conform with SVM, rename VMX specific Hyper-V files from "evmcs.{ch}"
to "hyperv.{ch}". While Enlightened VMCS is a lion's share of these
files, some stuff (e.g. enlightened MSR bitmap, the upcoming Hyper-V
L2 TLB flush, ...) goes beyond that.

Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20221101145426.251680-7-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: VMX: Do not declare vmread_error() asmlinkage

There is no need to declare vmread_error() asmlinkage, its arguments
can be passed via registers for both 32-bit and 64-bit targets.
Function argument registers are considered call-clobbered registers,
they are saved in the trampoline just before the function call and
restored afterwards.

Dropping "asmlinkage" patch unifies trampoline function argument handling
between 32-bit and 64-bit targets and improves generated code for 32-bit
targets.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20220817144045.3206-1-ubizjak@gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: VMX: Prevent RSB underflow before vmenter

On VMX, there are some balanced returns between the time the guest's
SPEC_CTRL value is written, and the vmenter.

Balanced returns (matched by a preceding call) are usually ok, but it's
at least theoretically possible an NMI with a deep call stack could
empty the RSB before one of the returns.

For maximum paranoia, don't allow *any* returns (balanced or otherwise)
between the SPEC_CTRL write and the vmenter.

[ bp: Fix 32-bit build. ]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>

KVM: VMX: Provide vmread version using asm-goto-with-outputs

Use asm-goto-output for smaller fast path code.

Message-Id: <YbcbbGW2GcMx6KpD@hirez.programming.kicks-ass.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

x86/vmx: Remove .fixup usage

In the vmread exceptin path, use the, thus far, unused output register
to push the @fault argument onto the stack. This, in turn, enables the
exception handler to not do pushes and only modify that register when
an exception does occur.

As noted by Sean the input constraint needs to be changed to "=&r" to
avoid the value and field occupying the same register.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20211110101325.781308550@infradead.org

KVM: x86: Move declaration of kvm_spurious_fault() to x86.h

Move the declaration of kvm_spurious_fault() to KVM's "private" x86.h,
it should never be called by anything other than low level KVM code.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
[sean: rebased to a series without __ex()/__kvm_handle_fault_on_reboot()]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210809173955.1710866-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: x86: Kill off __ex() and __kvm_handle_fault_on_reboot()

Remove the __kvm_handle_fault_on_reboot() and __ex() macros now that all
VMX and SVM instructions use asm goto to handle the fault (or in the
case of VMREAD, completely custom logic). Drop kvm_spurious_fault()'s
asmlinkage annotation as __kvm_handle_fault_on_reboot() was the only
flow that invoked it from assembly code.

Cc: Uros Bizjak <ubizjak@gmail.com>
Cc: Like Xu <like.xu.linux@gmail.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210809173955.1710866-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: vmx: add mismatched size assertions in vmcs_check32()

Add compile-time assertions in vmcs_check32() to disallow accesses to
64-bit and 64-bit high fields via vmcs_{read,write}32(). Upper level KVM
code should never do partial accesses to VMCS fields. KVM handles the
split accesses automatically in vmcs_{read,write}64() when running as a
32-bit kernel.

Reviewed-and-tested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Haiwei Li <lihaiwei@tencent.com>
Message-Id: <20210409022456.23528-1-lihaiwei.kernel@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

KVM: VMX: Rename ops.h to vmx_ops.h

Rename ops.h to vmx_ops.h to allow adding a tdx_ops.h in the future
without causing massive confusion.

Trust Domain Extensions (TDX) is built on VMX, but KVM cannot directly
access the VMCS(es) for a TDX guest, thus TDX will need its own "ops"
implementation for wrapping the low level operations.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200923183112.3030-3-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>