From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7372E3B6BF1 for ; Thu, 23 Jul 2026 18:21:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.69 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784830918; cv=none; b=hIH8Fs+ntF7/YdOOLPwHtIV6B+tA1n1Hv3Iuf7rcz2/tQzj0D77rEev+uTNMQtgoCF96+XPzxVPZa2e75Yly14AOaVVcAeJYV8ocY+a/yzazJJMYtqmLOYtnWHtDZY4860uWJ3C1cLlZxfbmmbOCJgLqGurG7qAzqn2jHdlg7Y4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784830918; c=relaxed/simple; bh=0tb67XafB5UfHWrQ/N2Zv8/FnZ2jU3xBrAVpocbKjDE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=uLfx7Qw4sNl5bofIpJ76uyu1irUCSpEa4/yT3ySZAAnlW+W31Zd0dQjHiAOHhFkwWO1LYvEl4iY6YgeAK2ExPGX/Br1TZ/iUVl0fjY9euTbUflywog8L20FpAa41DlNBemRkzohWiM4eHLf+3fJhpaj93woK/tRKYHRhPNx8Yz8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--smostafa.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=nW1Aaqle; arc=none smtp.client-ip=209.85.128.69 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--smostafa.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="nW1Aaqle" Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-4957287363bso6601675e9.0 for ; Thu, 23 Jul 2026 11:21:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1784830911; x=1785435711; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=N52o3BVp773wN3Idd00jSA0m0Lpy2g57ImYGMyeejhc=; b=nW1AaqlePuddkWPD2G4pvYqCAvZXjfux6bKNj5CHAcoi/EqyMxK9N4g6e+KtzETT44 xKpXfJkC3D5qDti4rqw3TEujFq2iEFIMAnTDesMKw9fIPVX5L34F++eVcHEbPl3qfhYf zSsrNMheuX/iFpqGyzjNn2asKVTFx/nlhmFKUbUbmzpvnlci1tmeFiSxX+hB2vvcy7M8 tdZMCzTmLt28xSumE49ppcFtiWrZGfgUcI0uR2bAQ2mqcNX3XynzVfnun1467KFLvqbK m4tKOYOA5roratlqXMYKIvV9Dhp9HnK3zvbjMgaAdqUJq+uxcx+MYvvt7ds1rL6nruMC 4iSQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1784830911; x=1785435711; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=N52o3BVp773wN3Idd00jSA0m0Lpy2g57ImYGMyeejhc=; b=N13K5CHUJgDVmsCM4OLjxWrgDAhHI82ye7ZPiky7gxlA4qTYAICDBHj9jTksON+uxg 036Jw1uY2Jmhhf5ky5YGus61y3NBcx8qN+M5RuWcrtpgIzdJNdqBv+uDQZkm8zbJSxfs 5VHEbDUPlA85Qj6ZbtyfZ3F/vvx7xgXGo/mtxePILIzI8unwCaVa3vVhcDeYWzy+Bl42 X6pOIyeJ/m73Qz0MD7+9PQxFxqgDIDoGYsY/rsCIWdhC/Ovj9ZcSd9yn5n68O34ob3ur lFPHvH+Q5aaO+46FMkNwjdla7wxS3DLuF+DfI8a2vNqK0K6/CqLQsfwR1kThn9xFZDx7 eKEQ== X-Gm-Message-State: AOJu0YzkICwAHCTJ+l2NZwIbjgZJbHQprl/Ha7QQzDmgstQq/1+GvP1+ ozSLdbynijAB6jKdYm9nYToGSXG3DEYaiAb3JSLOX/kiDxDfJL4E2NWnBXL7uPHfOdaHm8M0px5 9PgH6+CnN/OLVKMVeXAo2UQCNEspkuVLFy7WVrXdqJQySWal8KrcCaAKYTMoqHeAHesIpI4jpjL UiNfbetDuYH2ZqnCiOXqN9A4b4L5dJ2RNr7T/o9+BkzXdTVYIM2tkTqiA= X-Received: from wrhm19.prod.google.com ([2002:a05:6000:1813:b0:472:9520:f359]) (user=smostafa job=prod-delivery.src-stubby-dispatcher) by 2002:a7b:c84c:0:b0:495:3eb2:b763 with SMTP id 5b1f17b1804b1-49573cffa2emr35967485e9.21.1784830911229; Thu, 23 Jul 2026 11:21:51 -0700 (PDT) Date: Thu, 23 Jul 2026 18:21:40 +0000 In-Reply-To: <20260723182140.4025575-1-smostafa@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260723182140.4025575-1-smostafa@google.com> X-Mailer: git-send-email 2.55.0.229.g6434b31f56-goog Message-ID: <20260723182140.4025575-3-smostafa@google.com> Subject: [RFC PATCH v2 2/2] KVM: arm64: Support BBM level 3 From: Mostafa Saleh To: linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org Cc: maz@kernel.org, oupton@kernel.org, seiden@linux.ibm.com, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, vdonnefort@google.com, tabba@google.com, sebastianene@google.com, keirf@google.com, linu.cherian@arm.com, Mostafa Saleh Content-Type: text/plain; charset="UTF-8" If the system supports hardware Break-Before-Make (BBM) level 3, use it to replace stage-2 PTEs directly. Otherwise, fall back to the software BBM sequence. For BBML3 the sequence is: 1) Get a reference count on the containing table for the new PTE. 2) Atomically update the PTE with the new valid descriptor. 3) Invalidate the TLB for the old PTE. 4) Drop the reference count holding the old PTE. One interesting case, as BBML3 will update the PTE atomically, it can only know it raced with another core at the point of the cmpxchg failing, unlike the SW implementation which locks the PTE first. And as we must issue CMOs to the new mapped page before the update, that means with BBML3 racing cores will issue redundant CMOs. To avoid this, limit BBML3 support for systems with DIC and FWB, which does not require CMOs. Signed-off-by: Mostafa Saleh --- arch/arm64/kvm/hyp/pgtable.c | 58 +++++++++++++++++++++++++++++++----- 1 file changed, 51 insertions(+), 7 deletions(-) diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index d670da8882a5..4644b596f020 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -835,10 +835,24 @@ static void stage2_clean_old_pte(const struct kvm_pgtable_visit_ctx *ctx, mm_ops->put_page(ctx->ptep); } +/* + * We assume that KVM will never change the OA of an active translation. + * If the host needs to move the backing PFN, it should do an explicit + * unmap to issue the required TLBI. + */ +static bool stage2_use_bbml3(void) +{ + return system_supports_bbml3() && + cpus_have_final_cap(ARM64_HAS_STAGE2_FWB) && + cpus_have_final_cap(ARM64_HAS_CACHE_DIC); +} + /** * stage2_try_break_pte() - Invalidates a pte according to the * 'break-before-make' requirements of the - * architecture. + * architecture, if BMML3 is supported it + * will be used, meaning that this function + * won't break the PTE. * * @ctx: context of the visited pte. * @mmu: stage-2 mmu @@ -854,6 +868,10 @@ static bool stage2_try_break_pte(const struct kvm_pgtable_visit_ctx *ctx, { kvm_pte_t locked_pte; + /* All handled in stage2_make_pte() */ + if (stage2_use_bbml3() && kvm_pte_valid(ctx->old)) + return true; + if (stage2_pte_is_locked(ctx->old)) { /* * Should never occur if this walker has exclusive access to the @@ -873,16 +891,35 @@ static bool stage2_try_break_pte(const struct kvm_pgtable_visit_ctx *ctx, return true; } -static void stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t new) +static bool stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s2_mmu *mmu, + kvm_pte_t new) { struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops; - WARN_ON(!stage2_pte_is_locked(*ctx->ptep)); - if (stage2_pte_is_counted(new)) mm_ops->get_page(ctx->ptep); + if (stage2_use_bbml3() && kvm_pte_valid(ctx->old)) { + /* + * Barrier is required because stage2_try_set_pte() uses + * WRITE_ONCE for non-shared walks, lacking release semantics + * used in the software BBM case. + */ + smp_wmb(); + if (!stage2_try_set_pte(ctx, new)) { + /* Raced with another core. */ + if (stage2_pte_is_counted(new)) + mm_ops->put_page(ctx->ptep); + return false; + } + + stage2_clean_old_pte(ctx, mmu); + return true; + } + + WARN_ON(!stage2_pte_is_locked(*ctx->ptep)); smp_store_release(ctx->ptep, new); + return true; } static bool stage2_unmap_defer_tlb_flush(struct kvm_pgtable *pgt) @@ -1014,7 +1051,8 @@ static int stage2_map_walker_try_leaf(const struct kvm_pgtable_visit_ctx *ctx, stage2_pte_executable(new)) mm_ops->icache_inval_pou(kvm_pte_follow(new, mm_ops), granule); - stage2_make_pte(ctx, new); + if (!stage2_make_pte(ctx, data->mmu, new)) + return -EAGAIN; return 0; } @@ -1069,7 +1107,10 @@ static int stage2_map_walk_leaf(const struct kvm_pgtable_visit_ctx *ctx, * will be mapped lazily. */ new = kvm_init_table_pte(childp, mm_ops); - stage2_make_pte(ctx, new); + if (!stage2_make_pte(ctx, data->mmu, new)) { + mm_ops->put_page(childp); + return -EAGAIN; + } return 0; } @@ -1560,7 +1601,10 @@ static int stage2_split_walker(const struct kvm_pgtable_visit_ctx *ctx, * writes the PTE using smp_store_release(). */ new = kvm_init_table_pte(childp, mm_ops); - stage2_make_pte(ctx, new); + if (!stage2_make_pte(ctx, mmu, new)) { + kvm_pgtable_stage2_free_unlinked(mm_ops, childp, level); + return -EAGAIN; + } return 0; } -- 2.55.0.229.g6434b31f56-goog