linux-kernel - Re: [PATCH] KVM: x86: use CPUID to locate host page table reserved bits

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Message-ID: <d46bd0a8-5743-4665-85ea-14351fd85cdd@redhat.com>
Date:   Wed, 4 Dec 2019 16:36:16 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: use CPUID to locate host page table reserved
 bits

On 04/12/19 16:29, Sean Christopherson wrote:
> 
> The extra bit of paranoia doesn't cost much, so play it safe?  E.g.:
> 
> 	if (unlikely(boot_cpu_data.extended_cpuid_level < 0x80000008)) {
> 		WARN_ON_ONCE(boot_cpu_has(X86_FEATURE_TME) || SME?);
> 		return boot_cpu_data.x86_phys_bits;
> 	}
> 
> 	return cpuid_eax(0x80000008) & 0xff;

Sounds good.  I wouldn't bother with the WARN even.

Paolo