linux-kernel - Re: [PATCH v4 4/6] KVM: x86: Bump hypercall stat prior to fully completing hypercall

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <ad240077-ca7a-4306-a06f-6cf57b3ce4f2@intel.com>
Date: Thu, 28 Nov 2024 11:24:25 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Tom Lendacky <thomas.lendacky@....com>, Binbin Wu
 <binbin.wu@...ux.intel.com>, Isaku Yamahata <isaku.yamahata@...el.com>,
 Kai Huang <kai.huang@...el.com>
Subject: Re: [PATCH v4 4/6] KVM: x86: Bump hypercall stat prior to fully
 completing hypercall

On 11/28/2024 8:43 AM, Sean Christopherson wrote:
> Increment the "hypercalls" stat for KVM hypercalls as soon as KVM knows
> it will skip the guest instruction, i.e. once KVM is committed to emulating
> the hypercall.  Waiting until completion adds no known value, and creates a
> discrepancy where the stat will be bumped if KVM exits to userspace as a
> result of trying to skip the instruction, but not if the hypercall itself
> exits.
> 
> Handling the stat in common code will also avoid the need for another
> helper to dedup code when TDX comes along (TDX needs a separate completion
> path due to GPR usage differences).

Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>

> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/x86.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 13fe5d6eb8f3..11434752b467 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9979,7 +9979,6 @@ static int complete_hypercall_exit(struct kvm_vcpu *vcpu)
>   	if (!is_64_bit_hypercall(vcpu))
>   		ret = (u32)ret;
>   	kvm_rax_write(vcpu, ret);
> -	++vcpu->stat.hypercalls;
>   	return kvm_skip_emulated_instruction(vcpu);
>   }
>   
> @@ -9990,6 +9989,8 @@ unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr,
>   {
>   	unsigned long ret;
>   
> +	++vcpu->stat.hypercalls;
> +
>   	trace_kvm_hypercall(nr, a0, a1, a2, a3);
>   
>   	if (!op_64_bit) {
> @@ -10070,7 +10071,6 @@ unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr,
>   	}
>   
>   out:
> -	++vcpu->stat.hypercalls;
>   	return ret;
>   }
>   EXPORT_SYMBOL_GPL(__kvm_emulate_hypercall);