linux-kernel - Re: [PATCH 3/4] KVM: selftests: Add VM_MODE_PXXV57

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Message-ID: <CALMp9eQ3VdsNVb73BfaL5=2z=W+8-3O5Nv=ucmK2D+_zKWbyxw@mail.gmail.com>
Date: Tue, 21 Oct 2025 15:37:10 -0700
From: Jim Mattson <jmattson@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Shuah Khan <shuah@...nel.org>, 
	Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>, 
	Andrew Jones <ajones@...tanamicro.com>, Claudio Imbrenda <imbrenda@...ux.ibm.com>, 
	"Pratik R. Sampat" <prsampat@....com>, Kai Huang <kai.huang@...el.com>, 
	Eric Auger <eric.auger@...hat.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 3/4] KVM: selftests: Add VM_MODE_PXXV57_4K VM mode

On Wed, Oct 15, 2025 at 5:40 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Wed, Oct 15, 2025, Sean Christopherson wrote:
> > On Wed, Sep 17, 2025, Jim Mattson wrote:
> > > Add a new VM mode, VM_MODE_PXXV57_4K, to support tests that require
> > > 5-level paging on x86. This mode sets up a 57-bit virtual address
> > > space and sets CR4.LA57 in the guest.
>
> Thinking about this more, unless it's _really_ painful, e.g. because tests assume
> 4-level paging or 48-bit non-canonical address, I would rather turn VM_MODE_PXXV48_4K
> into VM_MODE_PXXVXX_4K and have ____vm_create() create the "maximal" VM.  That
> way tests don't need to go out of their way just to use 5-level paging, e.g. a
> "TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_LA57))" is all that is needed.  It will also
> gives quite a bit of coverage for free, e.g. that save/restore works with and
> without 5-level paging (contrived example, but you get the point).
>
> The NONCANONICAL #define works for LA57, so hopefully making tests play nice with
> LA57 is straightforward?

I will see what I can do. :)