Sender: Paolo Bonzini <paolo.bonzini@gmail.com>
Message-ID: <022620db-13ad-8118-5296-ae2913d41f1f@redhat.com>
Date:   Mon, 13 Dec 2021 16:06:22 +0100
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Subject: Re: [PATCH 10/19] kvm: x86: Emulate WRMSR of guest IA32_XFD
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To:     Yang Zhong <yang.zhong@intel.com>, x86@kernel.org,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com
Cc:     seanjc@google.com, jun.nakajima@intel.com, kevin.tian@intel.com,
        jing2.liu@linux.intel.com, jing2.liu@intel.com
References: <20211208000359.2853257-1-yang.zhong@intel.com>
 <20211208000359.2853257-11-yang.zhong@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <20211208000359.2853257-11-yang.zhong@intel.com>
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On 12/8/21 01:03, Yang Zhong wrote:
> +		/*
> +		 * Update IA32_XFD to the guest value so #NM can be
> +		 * raised properly in the guest. Instead of directly
> +		 * writing the MSR, call a helper to avoid breaking
> +		 * per-cpu cached value in fpu core.
> +		 */
> +		fpregs_lock();
> +		current->thread.fpu.fpstate->xfd = data;

This is wrong, it should be written in vcpu->arch.guest_fpu.

> +		xfd_update_state(current->thread.fpu.fpstate);

This is okay though, so that KVM_SET_MSR will not write XFD and WRMSR will.

That said, I think xfd_update_state should not have an argument. 
current->thread.fpu.fpstate->xfd is the only fpstate that should be 
synced with the xfd_state per-CPU variable.

Paolo

> +		fpregs_unlock();