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

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Message-ID: <aPAnGDh2u5-VK7gs@google.com>
Date: Wed, 15 Oct 2025 15:58:32 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: Jim Mattson <jmattson@...gle.com>, 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, Yosry Ahmed wrote:
> On Wed, Sep 17, 2025 at 02:48:39PM -0700, 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.
> > 
> > Signed-off-by: Jim Mattson <jmattson@...gle.com>
> > ---
> >  .../testing/selftests/kvm/include/kvm_util.h  |  1 +
> >  tools/testing/selftests/kvm/lib/kvm_util.c    | 21 +++++++++++++++++
> >  .../testing/selftests/kvm/lib/x86/processor.c | 23 ++++++++++++-------
> >  tools/testing/selftests/kvm/lib/x86/vmx.c     |  7 +++---
> >  4 files changed, 41 insertions(+), 11 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> > index 23a506d7eca3..b6ea5d966715 100644
> > --- a/tools/testing/selftests/kvm/include/kvm_util.h
> > +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> > @@ -175,6 +175,7 @@ enum vm_guest_mode {
> >  	VM_MODE_P40V48_16K,
> >  	VM_MODE_P40V48_64K,
> >  	VM_MODE_PXXV48_4K,	/* For 48bits VA but ANY bits PA */
> > +	VM_MODE_PXXV57_4K,	/* For 48bits VA but ANY bits PA */
> >  	VM_MODE_P47V64_4K,
> >  	VM_MODE_P44V64_4K,
> >  	VM_MODE_P36V48_4K,
> > diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> > index c3f5142b0a54..6b0e499c6e91 100644
> > --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c
> > @@ -232,6 +232,7 @@ const char *vm_guest_mode_string(uint32_t i)
> >  		[VM_MODE_P40V48_16K]	= "PA-bits:40,  VA-bits:48, 16K pages",
> >  		[VM_MODE_P40V48_64K]	= "PA-bits:40,  VA-bits:48, 64K pages",
> >  		[VM_MODE_PXXV48_4K]	= "PA-bits:ANY, VA-bits:48,  4K pages",
> > +		[VM_MODE_PXXV57_4K]	= "PA-bits:ANY, VA-bits:57,  4K pages",
> >  		[VM_MODE_P47V64_4K]	= "PA-bits:47,  VA-bits:64,  4K pages",
> >  		[VM_MODE_P44V64_4K]	= "PA-bits:44,  VA-bits:64,  4K pages",
> >  		[VM_MODE_P36V48_4K]	= "PA-bits:36,  VA-bits:48,  4K pages",
> > @@ -259,6 +260,7 @@ const struct vm_guest_mode_params vm_guest_mode_params[] = {
> >  	[VM_MODE_P40V48_16K]	= { 40, 48,  0x4000, 14 },
> >  	[VM_MODE_P40V48_64K]	= { 40, 48, 0x10000, 16 },
> >  	[VM_MODE_PXXV48_4K]	= {  0,  0,  0x1000, 12 },
> > +	[VM_MODE_PXXV57_4K]	= {  0,  0,  0x1000, 12 },
> >  	[VM_MODE_P47V64_4K]	= { 47, 64,  0x1000, 12 },
> >  	[VM_MODE_P44V64_4K]	= { 44, 64,  0x1000, 12 },
> >  	[VM_MODE_P36V48_4K]	= { 36, 48,  0x1000, 12 },
> > @@ -358,6 +360,25 @@ struct kvm_vm *____vm_create(struct vm_shape shape)
> >  		vm->va_bits = 48;
> >  #else
> >  		TEST_FAIL("VM_MODE_PXXV48_4K not supported on non-x86 platforms");
> 
> We should probably update TEST_ASSERT(vm->va_bits == 48 || vm->va_bits == 57)
> above to only assert 48 bits now, right?

No, because CPUID reports the _max_ virtual address width.  In theory, the assert
could be ">= 48", but in practice x86-64 only supports 48-bit and 57-bit VAs, so
selftests are paranoid and are sanity checking KVM at the same time.