Re: [PATCH v2] KVM: selftests: Fix 32-bit truncation of vm_get_max_gfn()

From: Andrew Jones <drjones@redhat.com>
To: David Matlack <dmatlack@google.com>
Cc: kvm@vger.kernel.org, Venkatesh Srinivas <venkateshs@chromium.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Ben Gardon <bgardon@google.com>, Peter Xu <peterx@redhat.com>
Subject: Re: [PATCH v2] KVM: selftests: Fix 32-bit truncation of vm_get_max_gfn()
Date: Sat, 22 May 2021 12:59:18 +0200	[thread overview]
Message-ID: <20210522105918.krdukoxe7jd2df6a@gator> (raw)
In-Reply-To: <20210521173828.1180619-1-dmatlack@google.com>

On Fri, May 21, 2021 at 05:38:28PM +0000, David Matlack wrote:
> vm_get_max_gfn() casts vm->max_gfn from a uint64_t to an unsigned int,
> which causes the upper 32-bits of the max_gfn to get truncated.
> 
> Nobody noticed until now likely because vm_get_max_gfn() is only used
> as a mechanism to create a memslot in an unused region of the guest
> physical address space (the top), and the top of the 32-bit physical
> address space was always good enough.
> 
> This fix reveals a bug in memslot_modification_stress_test which was
> trying to create a dummy memslot past the end of guest physical memory.
> Fix that by moving the dummy memslot lower.
> 
> Fixes: 52200d0d944e ("KVM: selftests: Remove duplicate guest mode handling")
> Reviewed-by: Venkatesh Srinivas <venkateshs@chromium.org>
> Signed-off-by: David Matlack <dmatlack@google.com>
> ---
> 
> v1 -> v2:
>  - Added Venkatesh's R-b line.
>  - Used PRIx64 to print uint64_t instead of %lx.
> 
>  tools/testing/selftests/kvm/include/kvm_util.h |  2 +-
>  tools/testing/selftests/kvm/lib/kvm_util.c     |  2 +-
>  .../testing/selftests/kvm/lib/perf_test_util.c |  4 +++-
>  .../kvm/memslot_modification_stress_test.c     | 18 +++++++++++-------
>  4 files changed, 16 insertions(+), 10 deletions(-)
>

Reviewed-by: Andrew Jones <drjones@redhat.com>

Thanks,
drew