linux-kernel - Re: [PATCH 7/9] KVM: SVM: Treat exit_code as an unsigned 64-bit value through all of KVM

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Message-ID: <aRdKa9jVMt0Rn5tj@google.com>
Date: Fri, 14 Nov 2025 07:27:39 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, 
	"K. Y. Srinivasan" <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, 
	Dexuan Cui <decui@...rosoft.com>, kvm@...r.kernel.org, linux-hyperv@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Jim Mattson <jmattson@...gle.com>, 
	Yosry Ahmed <yosry.ahmed@...ux.dev>
Subject: Re: [PATCH 7/9] KVM: SVM: Treat exit_code as an unsigned 64-bit value
 through all of KVM

On Thu, Nov 13, 2025, Sean Christopherson wrote:
> Fix KVM's long-standing buggy handling of SVM's exit_code as a 32-bit
> value.  Per the APM and Xen commit d1bd157fbc ("Big merge the HVM
> full-virtualisation abstractions.") (which is arguably more trustworthy
> than KVM), offset 0x70 is a single 64-bit value:
> 
>   070h 63:0 EXITCODE
> 
> Track exit_code as a single u64 to prevent reintroducing bugs where KVM
> neglects to correctly set bits 63:32.
> 
> Fixes: 6aa8b732ca01 ("[PATCH] kvm: userspace interface")
> Cc: Jim Mattson <jmattson@...gle.com>
> Cc: Yosry Ahmed <yosry.ahmed@...ux.dev>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---

...

> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index e79bc9cb7162..4c7a5cd10990 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -781,7 +781,7 @@ TRACE_EVENT_KVM_EXIT(kvm_nested_vmexit);
>   * Tracepoint for #VMEXIT reinjected to the guest
>   */
>  TRACE_EVENT(kvm_nested_vmexit_inject,
> -	    TP_PROTO(__u32 exit_code,
> +	    TP_PROTO(__u64 exit_code,
>  		     __u64 exit_info1, __u64 exit_info2,
>  		     __u32 exit_int_info, __u32 exit_int_info_err, __u32 isa),
>  	    TP_ARGS(exit_code, exit_info1, exit_info2,

As pointed out by the test bot[*], the trace macro to print exit reasons needs
to use 64-bit variants to play nice with 32-bit builds.

And now I'm questioning all of my testing, because my build setup detects that
as well, _and_ the hyperv_svm_test selftest fails.  *sigh*

diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
index 4c7a5cd10990..0fd72ce83926 100644
--- a/arch/x86/kvm/trace.h
+++ b/arch/x86/kvm/trace.h
@@ -383,10 +383,10 @@ TRACE_EVENT(kvm_apic,
 #define kvm_print_exit_reason(exit_reason, isa)                                \
        (isa == KVM_ISA_VMX) ?                                          \
        __print_symbolic(exit_reason & 0xffff, VMX_EXIT_REASONS) :      \
-       __print_symbolic(exit_reason, SVM_EXIT_REASONS),                \
+       __print_symbolic64(exit_reason, SVM_EXIT_REASONS),              \
        (isa == KVM_ISA_VMX && exit_reason & ~0xffff) ? " " : "",       \
        (isa == KVM_ISA_VMX) ?                                          \
-       __print_flags(exit_reason & ~0xffff, " ", VMX_EXIT_REASON_FLAGS) : ""
+       __print_flags64(exit_reason & ~0xffff, " ", VMX_EXIT_REASON_FLAGS) : ""
 
 #define TRACE_EVENT_KVM_EXIT(name)                                          \
 TRACE_EVENT(name,  


[*] https://lore.kernel.org/all/202511141707.t4ad044J-lkp@intel.com