[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <5335d070-1489-4e85-804b-b063bfda3f47@intel.com>
Date: Wed, 9 Jul 2025 14:40:48 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Kai Huang <kai.huang@...el.com>, seanjc@...gle.com, pbonzini@...hat.com
Cc: kvm@...r.kernel.org, thomas.lendacky@....com, nikunj@....com,
bp@...en8.de, isaku.yamahata@...el.com, rick.p.edgecombe@...el.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] KVM: x86: Reject KVM_SET_TSC_KHZ VM ioctl when vCPU
has been created
On 7/9/2025 1:38 PM, Kai Huang wrote:
> Reject the KVM_SET_TSC_KHZ VM ioctl when there's vCPU has already been
> created.
>
> The VM scope KVM_SET_TSC_KHZ ioctl is used to set up the default TSC
> frequency that all subsequent created vCPUs use. It is only intended to
> be called before any vCPU is created. Allowing it to be called after
> that only results in confusion but nothing good.
>
> Note this is an ABI change. But currently in Qemu (the de facto
> userspace VMM) only TDX uses this VM ioctl, and it is only called once
> before creating any vCPU, therefore the risk of breaking userspace is
> pretty low.
>
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Kai Huang <kai.huang@...el.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
> arch/x86/kvm/x86.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 699ca5e74bba..e5e55d549468 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7194,6 +7194,10 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
> u32 user_tsc_khz;
>
> r = -EINVAL;
> +
> + if (kvm->created_vcpus)
> + goto out;
> +
> user_tsc_khz = (u32)arg;
>
> if (kvm_caps.has_tsc_control &&
Powered by blists - more mailing lists