linux-kernel - Re: [PATCH v6 00/12] SVM cleanup and INVPCID feature support

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Message-ID: <feabccbb-8e0f-83b0-64a7-b5e1988c4559@redhat.com>
Date:   Wed, 24 Mar 2021 22:59:29 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Borislav Petkov <bp@...en8.de>, Babu Moger <babu.moger@....com>,
        Hugh Dickins <hughd@...gle.com>
Cc:     Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        kvm list <kvm@...r.kernel.org>, Joerg Roedel <joro@...tes.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Makarand Sonare <makarandsonare@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH v6 00/12] SVM cleanup and INVPCID feature support

On 24/03/21 22:21, Borislav Petkov wrote:
>  	if (kaiser_enabled)
>   		invpcid_flush_one(X86_CR3_PCID_ASID_USER, addr);
> +	else
> +		asm volatile("invlpg (%0)" ::"r" (addr) : "memory");
> +
>   	invpcid_flush_one(X86_CR3_PCID_ASID_KERN, addr);
>   }

I think the kernel ASID flush can also be moved under the "if"?

> and the reason why it does, IMHO, is because on AMD, kaiser_enabled is
> false because AMD is not affected by Meltdown, which means, there's no
> user/kernel pagetables split.
> 
> And that also means, you have global TLB entries which means that if you
> look at that __native_flush_tlb_single() function, it needs to flush
> global TLB entries on CPUs with X86_FEATURE_INVPCID_SINGLE by doing an
> INVLPG in the kaiser_enabled=0 case. Errgo, the above hunk.

Makes sense.

Paolo