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Message-ID: <65bbf58d-f88b-c7d6-523b-6e35f4972bf2@redhat.com>
Date: Thu, 18 Jul 2019 10:22:50 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>,
Randy Dunlap <rdunlap@...radead.org>,
Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH v2 04/22] x86/kvm: Don't call kvm_spurious_fault() from
.fixup
On 18/07/19 03:36, Josh Poimboeuf wrote:
> After making a change to improve objtool's sibling call detection, it
> started showing the following warning:
>
> arch/x86/kvm/vmx/nested.o: warning: objtool: .fixup+0x15: sibling call from callable instruction with modified stack frame
>
> The problem is the ____kvm_handle_fault_on_reboot() macro. It does a
> fake call by pushing a fake RIP and doing a jump. That tricks the
> unwinder into printing the function which triggered the exception,
> rather than the .fixup code.
>
> Instead of the hack to make it look like the original function made the
> call, just change the macro so that the original function actually does
> make the call. This allows removal of the hack, and also makes objtool
> happy.
>
> I triggered a vmx instruction exception and verified that the stack
> trace is still sane:
>
> kernel BUG at arch/x86/kvm/x86.c:358!
> invalid opcode: 0000 [#1] SMP PTI
> CPU: 28 PID: 4096 Comm: qemu-kvm Not tainted 5.2.0+ #16
> Hardware name: Lenovo THINKSYSTEM SD530 -[7X2106Z000]-/-[7X2106Z000]-, BIOS -[TEE113Z-1.00]- 07/17/2017
> RIP: 0010:kvm_spurious_fault+0x5/0x10
> Code: 00 00 00 00 00 8b 44 24 10 89 d2 45 89 c9 48 89 44 24 10 8b 44 24 08 48 89 44 24 08 e9 d4 40 22 00 0f 1f 40 00 0f 1f 44 00 00 <0f> 0b 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 41 55 49 89 fd 41
> RSP: 0018:ffffbf91c683bd00 EFLAGS: 00010246
> RAX: 000061f040000000 RBX: ffff9e159c77bba0 RCX: ffff9e15a5c87000
> RDX: 0000000665c87000 RSI: ffff9e15a5c87000 RDI: ffff9e159c77bba0
> RBP: 0000000000000000 R08: 0000000000000000 R09: ffff9e15a5c87000
> R10: 0000000000000000 R11: fffff8f2d99721c0 R12: ffff9e159c77bba0
> R13: ffffbf91c671d960 R14: ffff9e159c778000 R15: 0000000000000000
> FS: 00007fa341cbe700(0000) GS:ffff9e15b7400000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fdd38356804 CR3: 00000006759de003 CR4: 00000000007606e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
> Call Trace:
> loaded_vmcs_init+0x4f/0xe0
> alloc_loaded_vmcs+0x38/0xd0
> vmx_create_vcpu+0xf7/0x600
> kvm_vm_ioctl+0x5e9/0x980
> ? __switch_to_asm+0x40/0x70
> ? __switch_to_asm+0x34/0x70
> ? __switch_to_asm+0x40/0x70
> ? __switch_to_asm+0x34/0x70
> ? free_one_page+0x13f/0x4e0
> do_vfs_ioctl+0xa4/0x630
> ksys_ioctl+0x60/0x90
> __x64_sys_ioctl+0x16/0x20
> do_syscall_64+0x55/0x1c0
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x7fa349b1ee5b
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Acked-by: Paolo Bonzini <pbonzini@...hat.com>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> v2: Fix ____kvm_handle_fault_on_reboot() comment [Paolo]
>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> ---
> arch/x86/include/asm/kvm_host.h | 34 ++++++++++++++++++---------------
> 1 file changed, 19 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 0cc5b611a113..8282b8d41209 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1496,25 +1496,29 @@ enum {
> #define kvm_arch_vcpu_memslots_id(vcpu) ((vcpu)->arch.hflags & HF_SMM_MASK ? 1 : 0)
> #define kvm_memslots_for_spte_role(kvm, role) __kvm_memslots(kvm, (role).smm)
>
> +asmlinkage void __noreturn kvm_spurious_fault(void);
> +
> /*
> * Hardware virtualization extension instructions may fault if a
> * reboot turns off virtualization while processes are running.
> - * Trap the fault and ignore the instruction if that happens.
> + * Usually after catching the fault we just panic; during reboot
> + * instead the instruction is ignored.
> */
> -asmlinkage void kvm_spurious_fault(void);
> -
> -#define ____kvm_handle_fault_on_reboot(insn, cleanup_insn) \
> - "666: " insn "\n\t" \
> - "668: \n\t" \
> - ".pushsection .fixup, \"ax\" \n" \
> - "667: \n\t" \
> - cleanup_insn "\n\t" \
> - "cmpb $0, kvm_rebooting \n\t" \
> - "jne 668b \n\t" \
> - __ASM_SIZE(push) " $666b \n\t" \
> - "jmp kvm_spurious_fault \n\t" \
> - ".popsection \n\t" \
> - _ASM_EXTABLE(666b, 667b)
> +#define ____kvm_handle_fault_on_reboot(insn, cleanup_insn) \
> + "666: \n\t" \
> + insn "\n\t" \
> + "jmp 668f \n\t" \
> + "667: \n\t" \
> + "call kvm_spurious_fault \n\t" \
> + "668: \n\t" \
> + ".pushsection .fixup, \"ax\" \n\t" \
> + "700: \n\t" \
> + cleanup_insn "\n\t" \
> + "cmpb $0, kvm_rebooting\n\t" \
> + "je 667b \n\t" \
> + "jmp 668b \n\t" \
> + ".popsection \n\t" \
> + _ASM_EXTABLE(666b, 700b)
>
> #define __kvm_handle_fault_on_reboot(insn) \
> ____kvm_handle_fault_on_reboot(insn, "")
>
Acked-by: Paolo Bonzini <pbonzini@...hat.com>
This has a side effect of adding a jump in a generally hot path, but
let's hope that the speculation gods for once help us.
Paolo
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