From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from esa9.hc1455-7.c3s2.iphmx.com (esa9.hc1455-7.c3s2.iphmx.com [139.138.36.223]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EA387313523 for ; Fri, 12 Jun 2026 04:07:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=139.138.36.223 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781237281; cv=none; b=KoTa3lZy6KIiynqqXsxP/jHr2pB9YnrDikxc2KHao2S2azA4QXXXDp5A7+3cLFhxKL1cZvYbHzP4D7aalvSuW8j6TEOYGXqnGZqUiOuTuR+EAqOMYzM1SHgGB9Ws9WX/+6ZwMzkaNqk0JQxRZIhTx/8HBA2MNSBZdqYE+mb97jI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781237281; c=relaxed/simple; bh=ABzEIZDD2jKBPDc5Y/2VBD3Ut+7r1stkLEvCBcmneRw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=PVhywJ62uTtP/14sg4mxTj7bAGaDJtC27cVNQXZzikUsiwdd1KRNHQ6x1qqFGV7uGdmmr53xBXcqQI3e4X2o7ciRMvA7g2X5tai1rhVnFL6L7Z55PgrR6DUGD/lfj4pNPV0aGQXhKKdAKbb6i1EHVC1QaF5Hk1cZ2CB1t2zzTRc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=fujitsu.com; spf=pass smtp.mailfrom=fujitsu.com; dkim=pass (2048-bit key) header.d=fujitsu.com header.i=@fujitsu.com header.b=CWiF3YQI; arc=none smtp.client-ip=139.138.36.223 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=fujitsu.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=fujitsu.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=fujitsu.com header.i=@fujitsu.com header.b="CWiF3YQI" DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=fujitsu.com; i=@fujitsu.com; q=dns/txt; s=fj2; t=1781237280; x=1812773280; h=date:from:to:cc:subject:message-id:references: mime-version:in-reply-to; bh=ABzEIZDD2jKBPDc5Y/2VBD3Ut+7r1stkLEvCBcmneRw=; b=CWiF3YQItCZ9HysFcmKa0RPZul5jFgikOt2nFIgdpXfbNlIfJkjW3+qG rdBEk2dOdqmgKeJI8D2GMv3F/C5FvtQZbjAjlB7l8Ga7a0w3KK7Dxwz98 qeH4zvQD6MDniP5JH96ZvXzDhKSWQJuIHSNVMkypGb4F2CbBAAcC6V4vQ dVIa4I3zS1lVmOS6wmX909ReFVPtBPxRe+YYOccv/PRZ9CRvA2AE0KCDv Jxa3dFRrzADzQyQVGx/YNJ2eL6fWo9VxNXR9GHSfpxGOS7nVN+TsvABKv DnXiTFMwLKFw2Q2DgEEXNxyInoOOVm9a2HV09D3grOCc9a2mWNU1rYNzg Q==; X-CSE-ConnectionGUID: MWOMKwVRQj2dfRs2ZXgcag== X-CSE-MsgGUID: jH/AcS4sQf+IzJnNS+giEA== X-IronPort-AV: E=McAfee;i="6800,10657,11813"; a="231245174" X-IronPort-AV: E=Sophos;i="6.24,200,1774278000"; d="scan'208";a="231245174" Received: from gmgwuk01.global.fujitsu.com ([172.187.114.235]) by esa9.hc1455-7.c3s2.iphmx.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Jun 2026 13:06:48 +0900 Received: from az2uksmgm1.o.css.fujitsu.com (unknown [10.151.22.198]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by gmgwuk01.global.fujitsu.com (Postfix) with ESMTPS id AF5161C01699 for ; Fri, 12 Jun 2026 04:06:47 +0000 (UTC) Received: from az2uksmom4.o.css.fujitsu.com (unknown [10.151.22.204]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by az2uksmgm1.o.css.fujitsu.com (Postfix) with ESMTPS id 69564968454 for ; Fri, 12 Jun 2026 04:06:47 +0000 (UTC) Received: from sm-arm-grace07 (unknown [10.124.178.20]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by az2uksmom4.o.css.fujitsu.com (Postfix) with ESMTPS id 91611405ED9; Fri, 12 Jun 2026 04:06:43 +0000 (UTC) Date: Fri, 12 Jun 2026 13:06:40 +0900 From: Itaru Kitayama To: Wei-Lin Chang Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Marc Zyngier , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon Subject: Re: [PATCH v2 2/2] KVM: arm64: nv: Expose shadow page tables in debugfs Message-ID: References: <20260317182638.1592507-1-weilin.chang@arm.com> <20260317182638.1592507-3-weilin.chang@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260317182638.1592507-3-weilin.chang@arm.com> Hi Wei Lin, On Tue, Mar 17, 2026 at 06:26:38PM +0000, Wei-Lin Chang wrote: > Exposing shadow page tables in debugfs improves the debugability and > testability of NV. With this patch a new directory "nested" is created > for each VM created if the host is NV capable. Within the directory each > valid s2 mmu will have its shadow page table exposed as a readable file > with the file name formatted as 0x-0x-s2-{en,dis}abled. The > creation and removal of the files happen at the points when an s2 mmu > becomes valid, or the context it represents change. In the future the > "nested" directory can also hold other NV related information. > > This is gated behind CONFIG_PTDUMP_STAGE2_DEBUGFS. > > Suggested-by: Marc Zyngier > Reviewed-by: Sebastian Ene > Signed-off-by: Wei-Lin Chang > --- > arch/arm64/include/asm/kvm_host.h | 9 +++++++++ > arch/arm64/include/asm/kvm_mmu.h | 4 ++++ > arch/arm64/kvm/nested.c | 6 +++++- > arch/arm64/kvm/ptdump.c | 27 +++++++++++++++++++++++++++ > 4 files changed, 45 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > index 5d5a3bbdb95e..52977c9a11c3 100644 > --- a/arch/arm64/include/asm/kvm_host.h > +++ b/arch/arm64/include/asm/kvm_host.h > @@ -217,6 +217,10 @@ struct kvm_s2_mmu { > */ > bool nested_stage2_enabled; > > +#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS > + struct dentry *shadow_pt_debugfs_dentry; > +#endif > + > /* > * true when this MMU needs to be unmapped before being used for a new > * purpose. > @@ -405,6 +409,11 @@ struct kvm_arch { > * the associated pKVM instance in the hypervisor. > */ > struct kvm_protected_vm pkvm; > + > +#ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS > + /* Nested virtualization info */ > + struct dentry *debugfs_nv_dentry; > +#endif > }; > > struct kvm_vcpu_fault_info { > diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h > index d968aca0461a..01e9c72d6aa7 100644 > --- a/arch/arm64/include/asm/kvm_mmu.h > +++ b/arch/arm64/include/asm/kvm_mmu.h > @@ -393,8 +393,12 @@ static inline bool kvm_supports_cacheable_pfnmap(void) > > #ifdef CONFIG_PTDUMP_STAGE2_DEBUGFS > void kvm_s2_ptdump_create_debugfs(struct kvm *kvm); > +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu); > +void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu); > #else > static inline void kvm_s2_ptdump_create_debugfs(struct kvm *kvm) {} > +static inline void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu) {} > +static inline void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu) {} > #endif /* CONFIG_PTDUMP_STAGE2_DEBUGFS */ > > #endif /* __ASSEMBLER__ */ > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c > index eeea5e692370..31d74ed8449e 100644 > --- a/arch/arm64/kvm/nested.c > +++ b/arch/arm64/kvm/nested.c > @@ -730,8 +730,10 @@ static struct kvm_s2_mmu *get_s2_mmu_nested(struct kvm_vcpu *vcpu) > kvm->arch.nested_mmus_next = (i + 1) % kvm->arch.nested_mmus_size; > > /* Make sure we don't forget to do the laundry */ > - if (kvm_s2_mmu_valid(s2_mmu)) > + if (kvm_s2_mmu_valid(s2_mmu)) { > + kvm_nested_s2_ptdump_remove_debugfs(s2_mmu); > s2_mmu->pending_unmap = true; > + } > > /* > * The virtual VMID (modulo CnP) will be used as a key when matching > @@ -745,6 +747,8 @@ static struct kvm_s2_mmu *get_s2_mmu_nested(struct kvm_vcpu *vcpu) > s2_mmu->tlb_vtcr = vcpu_read_sys_reg(vcpu, VTCR_EL2); > s2_mmu->nested_stage2_enabled = vcpu_read_sys_reg(vcpu, HCR_EL2) & HCR_VM; > > + kvm_nested_s2_ptdump_create_debugfs(s2_mmu); > + This function can sleep, so I get while running your shadow stage 2 KVM selftest a messge: [ 4408.411009] BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:1624 [ 4408.411075] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 164, name: shadow_stage2 [ 4408.411136] preempt_count: 2, expected: 0 [ 4408.411172] RCU nest depth: 0, expected: 0 [ 4408.411228] CPU: 1 UID: 0 PID: 164 Comm: shadow_stage2 Tainted: G W 7.1.0-rc2+ #48 PREEMPT(full) [ 4408.411336] Tainted: [W]=WARN [ 4408.411368] Hardware name: , BIOS [ 4408.411403] Call trace: [ 4408.411427] show_stack+0x24/0x50 (C) [ 4408.411524] dump_stack_lvl+0x90/0x158 [ 4408.411633] dump_stack+0x1c/0x38 [ 4408.411741] __might_resched+0x168/0x208 [ 4408.411839] __might_sleep+0x54/0xb0 [ 4408.411936] down_write+0x30/0xe8 [ 4408.412048] start_dirop+0x3c/0xc0 [ 4408.412149] simple_start_creating+0xb8/0xc8 [ 4408.412241] debugfs_start_creating.part.0+0x68/0x180 [ 4408.412375] __debugfs_create_file+0x80/0x1f8 [ 4408.412505] debugfs_create_file_full+0x28/0x68 [ 4408.412637] kvm_nested_s2_ptdump_create_debugfs+0xa0/0x108 [ 4408.412734] kvm_vcpu_load_hw_mmu+0x27c/0x320 [ 4408.412839] kvm_arch_vcpu_load+0x318/0x5a0 [ 4408.412971] kvm_emulate_nested_eret+0x148/0x3d8 [ 4408.413072] kvm_handle_eret+0x110/0x138 [ 4408.413190] handle_exit+0x6c/0x1e8 [ 4408.413306] kvm_arch_vcpu_ioctl_run+0x3c4/0xc90 [ 4408.413396] kvm_vcpu_ioctl+0x1a0/0xa68 [ 4408.413508] __arm64_sys_ioctl+0xd0/0x160 [L1] L2 exit[ 4408.413631] invoke_syscall+0xa8/0x138 [ 4408.413723] el0_svc_common.constprop.0+0x4c/0x140 [ 4408.413821] do_el0_svc+0x28/0x58 [ 4408.413911] el0_svc+0x48/0x230 [ 4408.414035] el0t_64_sync_handler+0xc0/0x108 [ 4408.414166] el0t_64_sync+0x1b4/0x1b8 I tried to move this function out under the KVM MMU lock, but then I see a debug entry is duplicated error. I am not sure where exactly this nested stage 2 debugfs entry create function should go, your help is much appreciated. Thanks, Itaru. > out: > atomic_inc(&s2_mmu->refcnt); > > diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c > index 98763b291956..aebbbad85d38 100644 > --- a/arch/arm64/kvm/ptdump.c > +++ b/arch/arm64/kvm/ptdump.c > @@ -10,12 +10,14 @@ > #include > #include > > +#include > #include > #include > #include > > #define MARKERS_LEN 2 > #define KVM_PGTABLE_MAX_LEVELS (KVM_PGTABLE_LAST_LEVEL + 1) > +#define S2FNAMESZ sizeof("0x0123456789abcdef-0x0123456789abcdef-s2-disabled") > > struct kvm_ptdump_guest_state { > struct kvm_s2_mmu *mmu; > @@ -277,6 +279,28 @@ static const struct file_operations kvm_pgtable_levels_fops = { > .release = kvm_pgtable_debugfs_close, > }; > > +void kvm_nested_s2_ptdump_create_debugfs(struct kvm_s2_mmu *mmu) > +{ > + struct dentry *dent; > + char file_name[S2FNAMESZ]; > + > + snprintf(file_name, sizeof(file_name), "0x%llx-0x%llx-s2-%sabled", > + mmu->tlb_vttbr, > + mmu->tlb_vtcr, > + mmu->nested_stage2_enabled ? "en" : "dis"); > + > + dent = debugfs_create_file(file_name, 0400, > + mmu->arch->debugfs_nv_dentry, mmu, > + &kvm_ptdump_guest_fops); > + > + mmu->shadow_pt_debugfs_dentry = dent; > +} > + > +void kvm_nested_s2_ptdump_remove_debugfs(struct kvm_s2_mmu *mmu) > +{ > + debugfs_remove(mmu->shadow_pt_debugfs_dentry); > +} > + > void kvm_s2_ptdump_create_debugfs(struct kvm *kvm) > { > debugfs_create_file("stage2_page_tables", 0400, kvm->debugfs_dentry, > @@ -285,4 +309,7 @@ void kvm_s2_ptdump_create_debugfs(struct kvm *kvm) > &kvm->arch.mmu, &kvm_pgtable_range_fops); > debugfs_create_file("stage2_levels", 0400, kvm->debugfs_dentry, > &kvm->arch.mmu, &kvm_pgtable_levels_fops); > + if (cpus_have_final_cap(ARM64_HAS_NESTED_VIRT)) > + kvm->arch.debugfs_nv_dentry = > + debugfs_create_dir("nested", kvm->debugfs_dentry); > } > -- > 2.43.0 >