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From: Oliver Upton To: Sean Christopherson Cc: Marc Zyngier , James Morse , Alexandru Elisei , Paolo Bonzini , Shuah Khan , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, kvmarm@lists.linux.dev, Ricardo Koller , linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 4/7] KVM: selftests: Correctly initialize the VA space for TTBR0_EL1 Message-ID: References: <20221209015307.1781352-1-oliver.upton@linux.dev> <20221209015307.1781352-5-oliver.upton@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, Dec 09, 2022 at 08:45:01PM +0000, Sean Christopherson wrote: > On Fri, Dec 09, 2022, Oliver Upton wrote: > > An interesting feature of the Arm architecture is that the stage-1 MMU > > supports two distinct VA regions, controlled by TTBR{0,1}_EL1. As KVM > > selftests on arm64 only uses TTBR0_EL1, the VA space is constrained to > > [0, 2^(va_bits)). This is different from other architectures that > > allow for addressing low and high regions of the VA space from a single > > page table. > > > > KVM selftests' VA space allocator presumes the valid address range is > > split between low and high memory based the MSB, which of course is a > > poor match for arm64's TTBR0 region. > > > > Add a helper that correctly handles both addressing schemes with a > > comment describing each. > > > > Signed-off-by: Oliver Upton > > --- > > Thanks much! Looks awesome, especially the comment! > > Reviewed-by: Sean Christopherson ty! > > .../selftests/kvm/include/kvm_util_base.h | 1 + > > tools/testing/selftests/kvm/lib/kvm_util.c | 49 ++++++++++++++++--- > > 2 files changed, 44 insertions(+), 6 deletions(-) > > > > diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h > > index 6cd86da698b3..b193863d754f 100644 > > --- a/tools/testing/selftests/kvm/include/kvm_util_base.h > > +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h > > @@ -103,6 +103,7 @@ struct kvm_vm { > > struct sparsebit *vpages_mapped; > > bool has_irqchip; > > bool pgd_created; > > + bool has_split_va_space; > > vm_paddr_t ucall_mmio_addr; > > vm_paddr_t pgd; > > vm_vaddr_t gdt; > > diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c > > index a256ec67aff6..53d15f32f220 100644 > > --- a/tools/testing/selftests/kvm/lib/kvm_util.c > > +++ b/tools/testing/selftests/kvm/lib/kvm_util.c > > @@ -186,6 +186,43 @@ const struct vm_guest_mode_params vm_guest_mode_params[] = { > > _Static_assert(sizeof(vm_guest_mode_params)/sizeof(struct vm_guest_mode_params) == NUM_VM_MODES, > > "Missing new mode params?"); > > > > +/* > > + * Initializes vm->vpages_valid to match the canonical VA space of the > > + * architecture. > > + * > > + * Most architectures split the range addressed by a single page table into a > > + * low and high region based on the MSB of the VA. On architectures with this > > + * behavior the VA region spans [0, 2^(va_bits - 1)), [-(2^(va_bits - 1), -1]. > > + * > > + * arm64 is a bit different from the rest of the crowd, as the low and high > > + * regions of the VA space are addressed by distinct paging structures > > + * (TTBR{0,1}_EL1). > > Oooh, they're different CR3s in x86 terminology? Right, we can have two active table roots at any given time, each mapping their own portion of the address space. -- Thanks, Oliver