Saves one byte in __vmx_vcpu_run for the same functionality.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Message-Id: <20201029140457.126965-1-ubizjak@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Move the asm blob that invokes the appropriate IRQ handler after VM-Exit
into a proper subroutine. Unconditionally create a stack frame in the
subroutine so that, as objtool sees things, the function has standard
stack behavior. The dynamic stack adjustment makes using unwind hints
problematic.
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200915191505.10355-2-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Move the functions which are inside the RCU off region into the
non-instrumentable text section.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20200708195322.037311579@linutronix.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
POP [mem] defaults to the word size, and the only legal non-default
size is 16 bits, e.g. a 32-bit POP will #UD in 64-bit mode and vice
versa, no need to use __ASM_SIZE macro to force operating mode.
Changes since v1:
- Fix commit message.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Message-Id: <20200427205035.1594232-1-ubizjak@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Clear CF and ZF in the VM-Exit path after doing __FILL_RETURN_BUFFER so
that KVM doesn't interpret clobbered RFLAGS as a VM-Fail. Filling the
RSB has always clobbered RFLAGS, its current incarnation just happens
clear CF and ZF in the processs. Relying on the macro to clear CF and
ZF is extremely fragile, e.g. commit 089dd8e531 ("x86/speculation:
Change FILL_RETURN_BUFFER to work with objtool") tweaks the loop such
that the ZF flag is always set.
Reported-by: Qian Cai <cai@lca.pw>
Cc: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: stable@vger.kernel.org
Fixes: f2fde6a5bc ("KVM: VMX: Move RSB stuffing to before the first RET after VM-Exit")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200506035355.2242-1-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
The exception trampoline in .fixup section is not needed, the exception
handling code can jump directly to the label in the .text section.
Changes since v1:
- Fix commit message.
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Message-Id: <20200406202108.74300-1-ubizjak@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add a hand coded assembly trampoline to preserve volatile registers
across vmread_error(), and to handle the calling convention differences
between 64-bit and 32-bit due to asmlinkage on vmread_error(). Pass
@field and @fault on the stack when invoking the trampoline to avoid
clobbering volatile registers in the context of the inline assembly.
Calling vmread_error() directly from inline assembly is partially broken
on 64-bit, and completely broken on 32-bit. On 64-bit, it will clobber
%rdi and %rsi (used to pass @field and @fault) and any volatile regs
written by vmread_error(). On 32-bit, asmlinkage means vmread_error()
expects the parameters to be passed on the stack, not via regs.
Opportunistically zero out the result in the trampoline to save a few
bytes of code for every VMREAD. A happy side effect of the trampoline
is that the inline code footprint is reduced by three bytes on 64-bit
due to PUSH/POP being more efficent (in terms of opcode bytes) than MOV.
Fixes: 6e2020977e ("KVM: VMX: Add error handling to VMREAD helper")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200326160712.28803-1-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Registers in "regs" array are indexed as rax/rcx/rdx/.../rsi/rdi/r8/...
Reorder access to "regs" array in vmenter.S to follow its natural order.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
These are all functions which are invoked from elsewhere, so annotate
them as global using the new SYM_FUNC_START and their ENDPROC's by
SYM_FUNC_END.
Make sure ENTRY/ENDPROC is not defined on X86_64, given these were the
last users.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> [hibernate]
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> [xen bits]
Acked-by: Herbert Xu <herbert@gondor.apana.org.au> [crypto]
Cc: Allison Randal <allison@lohutok.net>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Andy Shevchenko <andy@infradead.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Armijn Hemel <armijn@tjaldur.nl>
Cc: Cao jin <caoj.fnst@cn.fujitsu.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Enrico Weigelt <info@metux.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Len Brown <len.brown@intel.com>
Cc: linux-arch@vger.kernel.org
Cc: linux-crypto@vger.kernel.org
Cc: linux-efi <linux-efi@vger.kernel.org>
Cc: linux-efi@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: platform-driver-x86@vger.kernel.org
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Wei Huang <wei@redhat.com>
Cc: x86-ml <x86@kernel.org>
Cc: xen-devel@lists.xenproject.org
Cc: Xiaoyao Li <xiaoyao.li@linux.intel.com>
Link: https://lkml.kernel.org/r/20191011115108.12392-25-jslaby@suse.cz
Fix an incorrect/stale comment regarding the vmx_vcpu pointer, as guest
registers are now loaded using a direct pointer to the start of the
register array.
Opportunistically add a comment to document why the vmx_vcpu pointer is
needed, its consumption via 'call vmx_update_host_rsp' is rather subtle.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Objtool reports the following:
arch/x86/kvm/vmx/vmenter.o: warning: objtool: vmx_vmenter()+0x14: call without frame pointer save/setup
But frame pointers are necessarily broken anyway, because
__vmx_vcpu_run() clobbers RBP with the guest's value before calling
vmx_vmenter(). So calling without a frame pointer doesn't make things
any worse.
Make objtool happy by changing the call to a UD2.
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lkml.kernel.org/r/9fc2216c9dc972f95bb65ce2966a682c6bda1cb0.1563413318.git.jpoimboe@redhat.com
The not-so-recent change to move VMX's VM-Exit handing to a dedicated
"function" unintentionally exposed KVM to a speculative attack from the
guest by executing a RET prior to stuffing the RSB. Make RSB stuffing
happen immediately after VM-Exit, before any unpaired returns.
Alternatively, the VM-Exit path could postpone full RSB stuffing until
its current location by stuffing the RSB only as needed, or by avoiding
returns in the VM-Exit path entirely, but both alternatives are beyond
ugly since vmx_vmexit() has multiple indirect callers (by way of
vmx_vmenter()). And putting the RSB stuffing immediately after VM-Exit
makes it much less likely to be re-broken in the future.
Note, the cost of PUSH/POP could be avoided in the normal flow by
pairing the PUSH RAX with the POP RAX in __vmx_vcpu_run() and adding an
a POP to nested_vmx_check_vmentry_hw(), but such a weird/subtle
dependency is likely to cause problems in the long run, and PUSH/POP
will take all of a few cycles, which is peanuts compared to the number
of cycles required to fill the RSB.
Fixes: 453eafbe65 ("KVM: VMX: Move VM-Enter + VM-Exit handling to non-inline sub-routines")
Reported-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Move the clearing of the common registers (not 64-bit-only) to the start
of the flow that clears registers holding guest state. This is
purely a cosmetic change so that the label doesn't point at a blank line
and a #define.
No functional change intended.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
...to make it callable from C code.
Note that because KVM chooses to be ultra paranoid about guest register
values, all callee-save registers are still cleared after VM-Exit even
though the host's values are now reloaded from the stack.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
...to prepare for making the assembly sub-routine callable from C code.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
...to prepare for making the sub-routine callable from C code.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
...to prepare for making the sub-routine callable from C code. That
means returning the result in RAX. Since RAX will be used to return the
result, use it as the scratch register as well to make the code readable
and to document that the scratch register is more or less arbitrary.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
...now that the name is no longer usurped by a defunct helper function.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
As evidenced by the myriad patches leading up to this moment, using
an inline asm blob for vCPU-run is nothing short of horrific. It's also
been called "unholy", "an abomination" and likely a whole host of other
names that would violate the Code of Conduct if recorded here and now.
The code is relocated nearly verbatim, e.g. quotes, newlines, tabs and
__stringify need to be dropped, but other than those cosmetic changes
the only functional changees are to add the "call" and replace the final
"jmp" with a "ret".
Note that STACK_FRAME_NON_STANDARD is also dropped from __vmx_vcpu_run().
Suggested-by: Andi Kleen <ak@linux.intel.com>
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Transitioning to/from a VMX guest requires KVM to manually save/load
the bulk of CPU state that the guest is allowed to direclty access,
e.g. XSAVE state, CR2, GPRs, etc... For obvious reasons, loading the
guest's GPR snapshot prior to VM-Enter and saving the snapshot after
VM-Exit is done via handcoded assembly. The assembly blob is written
as inline asm so that it can easily access KVM-defined structs that
are used to hold guest state, e.g. moving the blob to a standalone
assembly file would require generating defines for struct offsets.
The other relevant aspect of VMX transitions in KVM is the handling of
VM-Exits. KVM doesn't employ a separate VM-Exit handler per se, but
rather treats the VMX transition as a mega instruction (with many side
effects), i.e. sets the VMCS.HOST_RIP to a label immediately following
VMLAUNCH/VMRESUME. The label is then exposed to C code via a global
variable definition in the inline assembly.
Because of the global variable, KVM takes steps to (attempt to) ensure
only a single instance of the owning C function, e.g. vmx_vcpu_run, is
generated by the compiler. The earliest approach placed the inline
assembly in a separate noinline function[1]. Later, the assembly was
folded back into vmx_vcpu_run() and tagged with __noclone[2][3], which
is still used today.
After moving to __noclone, an edge case was encountered where GCC's
-ftracer optimization resulted in the inline assembly blob being
duplicated. This was "fixed" by explicitly disabling -ftracer in the
__noclone definition[4].
Recently, it was found that disabling -ftracer causes build warnings
for unsuspecting users of __noclone[5], and more importantly for KVM,
prevents the compiler for properly optimizing vmx_vcpu_run()[6]. And
perhaps most importantly of all, it was pointed out that there is no
way to prevent duplication of a function with 100% reliability[7],
i.e. more edge cases may be encountered in the future.
So to summarize, the only way to prevent the compiler from duplicating
the global variable definition is to move the variable out of inline
assembly, which has been suggested several times over[1][7][8].
Resolve the aforementioned issues by moving the VMLAUNCH+VRESUME and
VM-Exit "handler" to standalone assembly sub-routines. Moving only
the core VMX transition codes allows the struct indexing to remain as
inline assembly and also allows the sub-routines to be used by
nested_vmx_check_vmentry_hw(). Reusing the sub-routines has a happy
side-effect of eliminating two VMWRITEs in the nested_early_check path
as there is no longer a need to dynamically change VMCS.HOST_RIP.
Note that callers to vmx_vmenter() must account for the CALL modifying
RSP, e.g. must subtract op-size from RSP when synchronizing RSP with
VMCS.HOST_RSP and "restore" RSP prior to the CALL. There are no great
alternatives to fudging RSP. Saving RSP in vmx_enter() is difficult
because doing so requires a second register (VMWRITE does not provide
an immediate encoding for the VMCS field and KVM supports Hyper-V's
memory-based eVMCS ABI). The other more drastic alternative would be
to use eschew VMCS.HOST_RSP and manually save/load RSP using a per-cpu
variable (which can be encoded as e.g. gs:[imm]). But because a valid
stack is needed at the time of VM-Exit (NMIs aren't blocked and a user
could theoretically insert INT3/INT1ICEBRK at the VM-Exit handler), a
dedicated per-cpu VM-Exit stack would be required. A dedicated stack
isn't difficult to implement, but it would require at least one page
per CPU and knowledge of the stack in the dumpstack routines. And in
most cases there is essentially zero overhead in dynamically updating
VMCS.HOST_RSP, e.g. the VMWRITE can be avoided for all but the first
VMLAUNCH unless nested_early_check=1, which is not a fast path. In
other words, avoiding the VMCS.HOST_RSP by using a dedicated stack
would only make the code marginally less ugly while requiring at least
one page per CPU and forcing the kernel to be aware (and approve) of
the VM-Exit stack shenanigans.
[1] cea15c24ca39 ("KVM: Move KVM context switch into own function")
[2] a3b5ba49a8 ("KVM: VMX: add the __noclone attribute to vmx_vcpu_run")
[3] 104f226bfd ("KVM: VMX: Fold __vmx_vcpu_run() into vmx_vcpu_run()")
[4] 95272c2937 ("compiler-gcc: disable -ftracer for __noclone functions")
[5] https://lkml.kernel.org/r/20181218140105.ajuiglkpvstt3qxs@treble
[6] https://patchwork.kernel.org/patch/8707981/#21817015
[7] https://lkml.kernel.org/r/ri6y38lo23g.fsf@suse.cz
[8] https://lkml.kernel.org/r/20181218212042.GE25620@tassilo.jf.intel.com
Suggested-by: Andi Kleen <ak@linux.intel.com>
Suggested-by: Martin Jambor <mjambor@suse.cz>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Martin Jambor <mjambor@suse.cz>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Uros Bizjak