From patchwork Thu Sep 28 17:32:03 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vincent Donnefort X-Patchwork-Id: 13403355 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 77C4DE732FE for ; Thu, 28 Sep 2023 17:32:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Cc:To:From:Subject:Message-ID: References:Mime-Version:In-Reply-To:Date:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=zrw7WR0VMagVAEB6QWMpZn67XQifwJA/Q9OARF1x0yo=; b=NkQYPBdUehYuYsWv1p84ddowr/ 86XQhTqkcX0tZ6i/QtreKU592z/lkBhtyg6NJC+9r+flV/qLpEgo0NinLfF1JYhOSilY4TlMQOWg+ DJjA2zHbmMy9C8FiepvYr3YMgRXC4xWV3NKrJdncgxqSDpilozvJt2JbwmFhBCCs8sTXIKqqvogfN A3lksYiP7FoZoGWxyCLASf448PErhiVfwUzW3lRvxqs7yaf8L+NeZaCgy7uEY5qEDfLStIFawos/F CsWkwtl1/q++4FE9ROuZ0KP3TRPJdcJSzzsuLCIFLLbE6j7GrP5F/2hOBNZZm2vfhMkbY17jEx6YJ Ngw9f0iw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qlusH-006Qvm-1Z; Thu, 28 Sep 2023 17:32:29 +0000 Received: from mail-yw1-x114a.google.com ([2607:f8b0:4864:20::114a]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qlus6-006QsX-2Y for linux-arm-kernel@lists.infradead.org; Thu, 28 Sep 2023 17:32:20 +0000 Received: by mail-yw1-x114a.google.com with SMTP id 00721157ae682-5a21c283542so30123847b3.3 for ; Thu, 28 Sep 2023 10:32:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1695922335; x=1696527135; darn=lists.infradead.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=0OrolHEhppSNqHfijRmLo8eiKiIO9HbxQQbiWJh4bXs=; b=O4ZLuVHu8cUFovWTRbzq7gej7AU5t+EJYDfFW2KYKWNLAJqmOQgYjPh+pVpy/vDbZt GFNp575JBBXunho/kTM+maLsywMuwUMiDtMuXO3byj9C1RuB2ugjqzG7ogCol++HMki3 gCnjDZC9WK+Nh942dI1E9IZTl6hi13bdlAV9D90Z5lyhJbGSOLgxSkL2NcufgQZuKO2G s7Wr+w6uZ7Ogtohl8kWnwCTiKH0dL6q5VKR+uC/+gVJ7MtHL1Mg2L+GDyOuMM0bsE19c KmmQ6/HlB3IQYU1uXMUr+UdWxL/rpFduSv/naWsXWwPvBtVnv55vI516cIElMlEIJmtQ 4URw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1695922335; x=1696527135; h=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; bh=0OrolHEhppSNqHfijRmLo8eiKiIO9HbxQQbiWJh4bXs=; b=NQvXPS5zdhRz8fQachfyHmkJ2Ta5VOZs11qm9rYkesBEIqXWR1+vPmQbRP+ppeCIpj 3s4GFI0BboIHdDSRGcRKPJa0e970fts34LsbsINi9IpIf/B9h7oIbRSPT68vETctqwO7 MBoUZPix6VK0weOrxrDdi8rKY8AjSdRTSIjzVIZ6inlQhvCI6t/YcsVqrEC63SRqtCNl 70gyUIA3aacZxPZCTosBMB5kHslD2PT3RkNyE/OGxC8cdldIQ2fXmKXCcsB6461Z/JSA 8i8JOe5eGW4xZdXsYbj6R3BjonJLB4YNdX2u3dctvf1bBDFnVXDTiQO8YXtiwW0Zcgxo 47IA== X-Gm-Message-State: AOJu0YzJ3ZHd7+nGYoca2ym8uNHWiLk3/sc0ULpPKw4/X5bMoKA6A6cC krMjyLIW/b652sS0d044xKOkMUL5g99qLxhr X-Google-Smtp-Source: AGHT+IF/Fa0Mh0oBH5WiyhZSx/am6vHeFH1SjUosji1bp+q9vgUSK9otdQ/l0ZJOkJ52EUgq+NqoKxRy+7XU3Ds2 X-Received: from vdonnefort.c.googlers.com ([fda3:e722:ac3:cc00:28:9cb1:c0a8:2eea]) (user=vdonnefort job=sendgmr) by 2002:a81:7e07:0:b0:59b:c811:a709 with SMTP id o7-20020a817e07000000b0059bc811a709mr29487ywn.0.1695922335176; Thu, 28 Sep 2023 10:32:15 -0700 (PDT) Date: Thu, 28 Sep 2023 18:32:03 +0100 In-Reply-To: <20230928173205.2826598-1-vdonnefort@google.com> Mime-Version: 1.0 References: <20230928173205.2826598-1-vdonnefort@google.com> X-Mailer: git-send-email 2.42.0.515.g380fc7ccd1-goog Message-ID: <20230928173205.2826598-2-vdonnefort@google.com> Subject: [PATCH v2 1/2] KVM: arm64: Do not transfer page refcount for THP adjustment From: Vincent Donnefort To: maz@kernel.org, oliver.upton@linux.dev Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kernel-team@android.com, will@kernel.org, willy@infradead.org, Vincent Donnefort X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230928_103218_982477_F43307EC X-CRM114-Status: GOOD ( 12.69 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org GUP affects a refcount common to all pages forming the THP. There is therefore no need to move the refcount from a tail to the head page. Under the hood it decrements and increments the same counter. Signed-off-by: Vincent Donnefort Reviewed-by: Gavin Shan diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c index 587a104f66c3..de5e5148ef5d 100644 --- a/arch/arm64/kvm/mmu.c +++ b/arch/arm64/kvm/mmu.c @@ -1295,28 +1295,8 @@ transparent_hugepage_adjust(struct kvm *kvm, struct kvm_memory_slot *memslot, if (sz < PMD_SIZE) return PAGE_SIZE; - /* - * The address we faulted on is backed by a transparent huge - * page. However, because we map the compound huge page and - * not the individual tail page, we need to transfer the - * refcount to the head page. We have to be careful that the - * THP doesn't start to split while we are adjusting the - * refcounts. - * - * We are sure this doesn't happen, because mmu_invalidate_retry - * was successful and we are holding the mmu_lock, so if this - * THP is trying to split, it will be blocked in the mmu - * notifier before touching any of the pages, specifically - * before being able to call __split_huge_page_refcount(). - * - * We can therefore safely transfer the refcount from PG_tail - * to PG_head and switch the pfn from a tail page to the head - * page accordingly. - */ *ipap &= PMD_MASK; - kvm_release_pfn_clean(pfn); pfn &= ~(PTRS_PER_PMD - 1); - get_page(pfn_to_page(pfn)); *pfnp = pfn; return PMD_SIZE;