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Thu, 11 Sep 2025 06:49:44 -0700 (PDT) From: Jack Thomson To: maz@kernel.org, oliver.upton@linux.dev, pbonzini@redhat.com Cc: joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, shuah@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, isaku.yamahata@intel.com, roypat@amazon.co.uk, kalyazin@amazon.co.uk, jackabt@amazon.com Subject: [PATCH 2/6] KVM: arm64: Add KVM_PGTABLE_WALK_PRE_FAULT walk flag Date: Thu, 11 Sep 2025 14:46:44 +0100 Message-Id: <20250911134648.58945-3-jackabt.amazon@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20250911134648.58945-1-jackabt.amazon@gmail.com> References: <20250911134648.58945-1-jackabt.amazon@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Jack Thomson Don't return -EAGAIN from stage2_map_walker_try_leaf during KVM_PRE_FAULT_MEMORY. During pre-faults, user_abort() is retried upon returning -EAGAIN, meaning the ioctl would get stuck in an infinite loop if userspace tries to pre-fault already existing mappings Signed-off-by: Jack Thomson --- arch/arm64/include/asm/kvm_pgtable.h | 3 +++ arch/arm64/kvm/hyp/pgtable.c | 6 +++++- 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/= kvm_pgtable.h index 2888b5d03757..0789671d1c4f 100644 --- a/arch/arm64/include/asm/kvm_pgtable.h +++ b/arch/arm64/include/asm/kvm_pgtable.h @@ -296,6 +296,8 @@ typedef bool (*kvm_pgtable_force_pte_cb_t)(u64 addr, u6= 4 end, * @KVM_PGTABLE_WALK_SKIP_CMO: Visit and update table entries * without Cache maintenance * operations required. + * @KVM_PGTABLE_WALK_PRE_FAULT Indicates the page-table walk was + * invoked from a pre-fault request. */ enum kvm_pgtable_walk_flags { KVM_PGTABLE_WALK_LEAF =3D BIT(0), @@ -305,6 +307,7 @@ enum kvm_pgtable_walk_flags { KVM_PGTABLE_WALK_HANDLE_FAULT =3D BIT(4), KVM_PGTABLE_WALK_SKIP_BBM_TLBI =3D BIT(5), KVM_PGTABLE_WALK_SKIP_CMO =3D BIT(6), + KVM_PGTABLE_WALK_PRE_FAULT =3D BIT(7), }; =20 struct kvm_pgtable_visit_ctx { diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index c351b4abd5db..140dccec2c5b 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -914,9 +914,13 @@ static int stage2_map_walker_try_leaf(const struct kvm= _pgtable_visit_ctx *ctx, * same mapping or only change the access permissions. Instead, * the vCPU will exit one more time from guest if still needed * and then go through the path of relaxing permissions. + * + * When walking in the context of a pre-fault request, if the + * mapping already exists we can return 0, as there's nothing + * to do. */ if (!stage2_pte_needs_update(ctx->old, new)) - return -EAGAIN; + return (ctx->flags & KVM_PGTABLE_WALK_PRE_FAULT) ? 0 : -EAGAIN; =20 /* If we're only changing software bits, then store them and go! */ if (!kvm_pgtable_walk_shared(ctx) && --=20 2.43.0