Re: [PATCH 0/2] 52-bit VA guest mode ID support

[Itaru Kitayama <itaru.kitayama@fujitsu.com>]

Hi Fuad,
On Fri, Sep 04, 2026 at 09:14:36AM +0100, Fuad Tabba wrote:
> On Tue, 25 Aug 2026 at 22:18, Itaru Kitayama <itaru.kitayama@fujitsu.com> wrote:
> >
> > This patch series extends the arm64 KVM selftest framework
> > to support 52-bit guest virtual address (VA) modes in addition to
> > the existing 52-bit physical address (PA) configurations.
> > The motivation is to enable validation of LPA2 guest memory-management
> > behaviour in configurations that use a 52-bit VA space.
> > While the selftest framework already supports testing 52-bit PA
> > configurations, it lacks the ability to exercise guests running with
> > 52-bit virtual addresses, leaving part of the LPA2 functionality untested.
> 
> The series adds three 52-bit VA guest modes, but nothing in tree maps
> a guest VA high enough to use them. The mode-iterating tests map at a
> fixed low GVA, so pgd_index() returns 0 and only the first entry of
> the top level is ever used.
> 
> What do you expect the modes to catch as they stand? The allocators
> already take a minimum GVA, so mapping high in one of those tests
> looks like a small change.

I think at least a 4KB page is allocated for the level -1 translation table, 
and entry 0 is populated with a Table descriptor pointing to the level 0 translation
table. But, no it does not test a nonzero top-level index.

> 
> > To address this, the series introduces new guest modes for 52-bit VA
> > operation, adds five-level page table support where required, and
> > performs runtime detection of host 52-bit VA capability so that
> > LPA2-enabled guest VA tests are executed only on supported systems.
> >
> > Testing:
> >
> > Built and tested on arm64.
> > Verified on QEMU with a V52-capable guest configuration.
> > Confirmed correct operation of high virtual address mappings by
> > exercising guest memory accesses in the 52-bit VA range.
> 
> I could not reproduce "exercising guest memory accesses in the 52-bit
> VA range" with anything in tree either. Could you say which test you
> ran, which guest modes, and on what?

I just in guest_code() of existing one of the kselftests, mapped and 
accessed a page at 1ULL << 49 using virt_pg_map() and on QEMU TCG mode
as I don't currently have access to the machines LPA and LPA2 features.

Thanks,
Itaru.
> 
> Thanks,
> /fuad
> 
> > Signed-off-by: Itaru Kitayama <itaru.kitayama@fujitsu.com>
> > Reviewed-by: Takayuki Okamoto <tokamoto@fujitsu.com>
> > ---
> > Itaru Kitayama (2):
> >       KVM: selftest: arm64: Support 5-level paging in stage 1 translation table
> >       KVM: selftests: arm64: Add 52-bit VA guest modes
> >
> >  .../selftests/kvm/include/arm64/processor.h        |  2 +
> >  tools/testing/selftests/kvm/include/kvm_util.h     |  3 +
> >  tools/testing/selftests/kvm/lib/arm64/processor.c  | 87 ++++++++++++++++++++--
> >  tools/testing/selftests/kvm/lib/guest_modes.c      |  5 ++
> >  tools/testing/selftests/kvm/lib/kvm_util.c         | 11 +++
> >  5 files changed, 103 insertions(+), 5 deletions(-)
> > ---
> > base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
> > change-id: 20260825-arm64-52bit-va-32f1f4cd050d
> >
> > Best regards,
> > --
> > Itaru Kitayama <itaru.kitayama@fujitsu.com>
> >