linux-kernel - Re: [RFC PATCH v5 027/104] KVM: TDX: initialize VM with TDX specific parameters

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Message-ID: <e392b53a-fbaa-4724-07f4-171424144f70@redhat.com>
Date:   Tue, 5 Apr 2022 14:58:04 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...il.com, Jim Mattson <jmattson@...gle.com>,
        erdemaktas@...gle.com, Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 027/104] KVM: TDX: initialize VM with TDX specific
 parameters

On 3/4/22 20:48, isaku.yamahata@...el.com wrote:
> +	td_params->attributes = init_vm->attributes;
> +	if (td_params->attributes & TDX_TD_ATTRIBUTE_PERFMON) {
> +		pr_warn("TD doesn't support perfmon. KVM needs to save/restore "
> +			"host perf registers properly.\n");
> +		return -EOPNOTSUPP;
> +	}

Why does KVM have to hardcode this (and LBR/AMX below)?  Is the level of 
hardware support available from tdx_caps, for example through the CPUID 
configs (0xA for this one, 0xD for LBR and AMX)?

> +	/* PT can be exposed to TD guest regardless of KVM's XSS support */
> +	guest_supported_xss &= (supported_xss | XFEATURE_MASK_PT);
> +	td_params->xfam = guest_supported_xcr0 | guest_supported_xss;
> +	if (td_params->xfam & TDX_TD_XFAM_LBR) {
> +		pr_warn("TD doesn't support LBR. KVM needs to save/restore "
> +			"IA32_LBR_DEPTH properly.\n");
> +		return -EOPNOTSUPP;
> +	}
> +
> +	if (td_params->xfam & TDX_TD_XFAM_AMX) {
> +		pr_warn("TD doesn't support AMX. KVM needs to save/restore "
> +			"IA32_XFD, IA32_XFD_ERR properly.\n");
> +		return -EOPNOTSUPP;
> +	}

> 
> +	if (init_vm->tsc_khz)
> +		guest_tsc_khz = init_vm->tsc_khz;
> +	else
> +		guest_tsc_khz = max_tsc_khz;

You can just use kvm->arch.default_tsc_khz in the latest kvm/queue.

> +#define BUILD_BUG_ON_MEMCPY(dst, src)				\
> +	do {							\
> +		BUILD_BUG_ON(sizeof(dst) != sizeof(src));	\
> +		memcpy((dst), (src), sizeof(dst));		\
> +	} while (0)
> +
> +	BUILD_BUG_ON_MEMCPY(td_params->mrconfigid, init_vm->mrconfigid);
> +	BUILD_BUG_ON_MEMCPY(td_params->mrowner, init_vm->mrowner);
> +	BUILD_BUG_ON_MEMCPY(td_params->mrownerconfig, init_vm->mrownerconfig);
> +


Please rename to MEMCPY_SAME_SIZE.

Thanks,

Paolo