linux-kernel - Re: [PATCH Part2 RFC v2 08/37] x86/sev: Split the physmap when adding the page in RMP table

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Message-ID: <c1e9573e-9be4-ee85-9363-73b9c60db315@intel.com>
Date:   Mon, 3 May 2021 08:41:49 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Andy Lutomirski <luto@...capital.net>,
        Brijesh Singh <brijesh.singh@....com>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH Part2 RFC v2 08/37] x86/sev: Split the physmap when adding
 the page in RMP table

On 5/3/21 8:15 AM, Andy Lutomirski wrote:
> How much performance do we get back if we add a requirement that only
> 2M pages (hugetlbfs, etc) may be used for private guest memory?

Are you generally asking about the performance overhead of using 4k
pages instead of 2M for the direct map?  We looked at that recently and
pulled together some data:

> https://lore.kernel.org/lkml/213b4567-46ce-f116-9cdf-bbd0c884eb3c@linux.intel.com/