linux-kernel - Re: [RFC PATCH v5 038/104] KVM: x86/mmu: Allow per-VM override of the TDP max page level

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Message-ID: <43098446667829fc592b7cc7d5fd463319d37562.camel@intel.com>
Date:   Sat, 02 Apr 2022 11:27:03 +1300
From:   Kai Huang <kai.huang@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>
Subject: Re: [RFC PATCH v5 038/104] KVM: x86/mmu: Allow per-VM override of
 the TDP max page level

On Fri, 2022-04-01 at 14:08 +0000, Sean Christopherson wrote:
> On Fri, Apr 01, 2022, Kai Huang wrote:
> > On Fri, 2022-03-04 at 11:48 -0800, isaku.yamahata@...el.com wrote:
> > > From: Sean Christopherson <sean.j.christopherson@...el.com>
> > > 
> > > In the existing x86 KVM MMU code, there is already max_level member in
> > > struct kvm_page_fault with KVM_MAX_HUGEPAGE_LEVEL initial value.  The KVM
> > > page fault handler denies page size larger than max_level.
> > > 
> > > Add per-VM member to indicate the allowed maximum page size with
> > > KVM_MAX_HUGEPAGE_LEVEL as default value and initialize max_level in struct
> > > kvm_page_fault with it.
> > > 
> > > For the guest TD, the set per-VM value for allows maximum page size to 4K
> > > page size.  Then only allowed page size is 4K.  It means large page is
> > > disabled.
> > 
> > Do not support large page for TD is the reason that you want this change, but
> > not the result.  Please refine a little bit.
> 
> Not supporting huge pages was fine for the PoC, but I'd prefer not to merge TDX
> without support for huge pages.  Has any work been put into enabling huge pages?
> If so, what's the technical blocker?  If not...

Hi Sean,

Is there any reason large page support must be included in the initial merge of
TDX?  Large page is more about performance improvement I think.  Given this
series is already very big, perhaps we can do it later.

-- 
Thanks,
-Kai