From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 DACFA348445; Thu, 16 Jul 2026 06:45:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784184308; cv=none; b=sseSQisfqgPixpUr6kIEwJjcayBOVsj8Uad5itgJg4pCIhKoq+bfiun7f5Rv5lacrRopjgYrhNI7Esu8PKRrXDHz+EXlKAB4ZQ9AKSSHAU+SvW8ubEmg2CWd8IZpbdaTKDDXyi86PiqvrZb1qQKAOezshzdcSotNwoNAvWpvayQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784184308; c=relaxed/simple; bh=B+RPWLmKBBJ+TxlNUSXj7Eof75EAU6oRG0hCLpmLyWw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jdC70sKPpeecxsDFVw9BZmChp3ETpjQouEJ8deBAjvj7wf/dTSenfumGtQxwL0tPrGrfbF6ui2RJIrcB0wJm2XIeMX7D7lfMAGaGTTxJf2yqWk5YXpHwwnGgv4vtzqC9gUwvB8/Y+re3ShV79t2fXJZ4xvbz+DM9Lb8VgO+GXcU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Madks8dW; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Madks8dW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 59D491F000E9; Thu, 16 Jul 2026 06:45:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784184306; bh=19yKS+O/fpA2riFL7dxV6VygyRkDnrquIviX6BjC4RY=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=Madks8dWlCdHfXJHxmAGI0CG2hqP5O5PJ1vfQVltwDeXMqF4CoUFAqybtIOY2nwVe uHATZgU5Qn0zMOMhoze6BRx0aWylcMik1TiHczQIW82px6rKfKPYfj3yFg36qUEjyG lZ1IxPvzq8kVAuaZYhJ3TCYkSfoy7Rgg7Y7LCVK+uOShbfc1ckL1GwjuZ3AHgMd/tT 3C6SDWvJ/s9AQeCwQjWwHjoyN24JukT25dI6VK5vvhrrKTFDfcD7ugDCPbr2/lLU7m jo+NEhTYaPr098lFoug+ZzljiYICRLxYsp+M95bk9aLhMDDCoErGDbEP6RHTDhOIjE EYFIHMesz26KA== Date: Wed, 15 Jul 2026 23:45:05 -0700 From: Oliver Upton To: Wei-Lin Chang Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Marc Zyngier , Fuad Tabba , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Itaru Kitayama , Sebastian Ene Subject: Re: [PATCH v4 3/6] KVM: arm64: nv: Add nested revmap broken tracepoint Message-ID: References: <20260714115926.2044757-1-weilin.chang@arm.com> <20260714115926.2044757-4-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: <20260714115926.2044757-4-weilin.chang@arm.com> Hi Wei-Lin, On Tue, Jul 14, 2026 at 12:59:22PM +0100, Wei-Lin Chang wrote: > Add a tracepoint to track when a nested reverse map becomes broken. This > makes it easier to detect NV performance degradation caused by full > shadow stage-2 unmaps. > > Signed-off-by: Wei-Lin Chang I'm not too excited about making a tracepoint out of this, especially since a 'broken' reverse map is more of a KVM implementation detail (that could change) than anything else. BPF is quite popular at this point, do you think it's reasonable to instead expect the curious KVM developer to attach a kprobe and inspect the state of the nested MMU? Thanks, Oliver > --- > arch/arm64/kvm/nested.c | 7 ++++++- > arch/arm64/kvm/trace_arm.h | 27 +++++++++++++++++++++++++++ > 2 files changed, 33 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c > index 065823e415ce..22f8a1daca93 100644 > --- a/arch/arm64/kvm/nested.c > +++ b/arch/arm64/kvm/nested.c > @@ -17,6 +17,7 @@ > #include > > #include "sys_regs.h" > +#include "trace.h" > > struct vncr_tlb { > /* The guest's VNCR_EL2 */ > @@ -916,8 +917,12 @@ void kvm_record_nested_revmap(gpa_t canonical_ipa, struct kvm_s2_mmu *mmu, > > mas_set_range(&mas_rmap, canonical_ipa, canonical_ipa_end); > if (mas_store_gfp(&mas_rmap, xa_mk_value(new_entry), > - GFP_NOWAIT | __GFP_ACCOUNT)) > + GFP_NOWAIT | __GFP_ACCOUNT)) { > + trace_kvm_nested_revmap_broken(mmu - mmu->arch->nested_mmus, > + canonical_ipa, canonical_ipa_end, > + nested_ipa, new_entry); > mmu->nested_revmap_broken = true; > + } > unlock: > mtree_unlock(revmap_mt); > } > diff --git a/arch/arm64/kvm/trace_arm.h b/arch/arm64/kvm/trace_arm.h > index 9c60f6465c78..0db90068ff63 100644 > --- a/arch/arm64/kvm/trace_arm.h > +++ b/arch/arm64/kvm/trace_arm.h > @@ -415,6 +415,33 @@ TRACE_EVENT(kvm_forward_sysreg_trap, > sys_reg_Op2(__entry->sysreg)) > ); > > +TRACE_EVENT(kvm_nested_revmap_broken, > + TP_PROTO(int mmu_idx, unsigned long canonical_ipa, > + unsigned long canonical_ipa_end, unsigned long nested_ipa, > + unsigned long revmap_entry), > + TP_ARGS(mmu_idx, canonical_ipa, canonical_ipa_end, nested_ipa, revmap_entry), > + > + TP_STRUCT__entry( > + __field(int, mmu_idx) > + __field(unsigned long, canonical_ipa) > + __field(unsigned long, nested_ipa) > + __field(size_t, size) > + __field(unsigned long, revmap_entry) > + ), > + > + TP_fast_assign( > + __entry->mmu_idx = mmu_idx; > + __entry->canonical_ipa = canonical_ipa; > + __entry->nested_ipa = nested_ipa; > + __entry->size = canonical_ipa_end - canonical_ipa + 1; > + __entry->revmap_entry = revmap_entry; > + ), > + > + TP_printk("mmu idx: %d, cipa: 0x%016lx, nipa: 0x%016lx, size: 0x%016lx, entry: %016lx", > + __entry->mmu_idx, __entry->canonical_ipa, __entry->nested_ipa, > + __entry->size, __entry->revmap_entry) > +); > + > #endif /* _TRACE_ARM_ARM64_KVM_H */ > > #undef TRACE_INCLUDE_PATH > -- > 2.43.0 >