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 3582A39FCD8; Tue, 2 Jun 2026 21:26:45 +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=1780435607; cv=none; b=UN3W4mbERe85TLM1ga0BAD42UVISfYxJIt1xq4TXM6/5flqXIfoV5/IdI7uOt/ulbHtJ8R+izWisJE+15FTAM/4ml3+Tgg/oML7pnfxwSsogZlWwBqNHSRlsZ48rFQ2iyh/gxlUyZ5fwg07z2aUhNjQl2NP9oOuaGA84FfBxJCc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780435607; c=relaxed/simple; bh=d4n5Bid4CGYWzFjvUI7PZkjkb1uPv28ufUeP5I/d+bU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=R8fNQoxQFUDOcaebcEWPjK0YH8XN3HFBenWrxA2ZVDQagOGn9xlVVzwV2pf3Mf9cZw8h23NRKlaO6VP5OvSKohB4uv0EF2ASq9RIMymrh7SrijCkUlBzT8HuLZWERIDjtI4QwIGIRqTEQUufOQjHphnMSvkPV2fSSQIEOMfZck8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KFwHDOgF; 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="KFwHDOgF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9D6DD1F0089B; Tue, 2 Jun 2026 21:26:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780435605; bh=ze0kNDk6g2fIlh+GS7Z/yQ6VYddrJB+PKpzcEjeF1PU=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=KFwHDOgFvIhGuQcI+ESC5fZw6qjE8ld7genCRd/zpNjBooCmQS5a0A/NAntHb9aNl 7HPL4It0xnAM9X5Rn2oeMnoTHUWVDv3/pxh0qCql2xq1tS/eQDES3Hss0tsZqlrL4r iCmxBdnQwfk/uVoIei8Iuz5ghvmKZ+vTQ3JVEkq0Lf3UErTx6YwGhhV3Wm6JcPSXZz bUW5/pTfsD7XocB2uKoZYFTnPX6z8YN9Cz7iJVD0dy8I+IinFopnCMZSj2hkoSCDt9 PiG4pFn4T+tcX21l20/ursTZXm6L8pULwJSI5i3+ZMQhQXvq7+xvXV5RxYkN7IuCY0 6I289whe+O/XA== Date: Tue, 2 Jun 2026 14:26:44 -0700 From: Oliver Upton To: Hyunwoo Kim Cc: maz@kernel.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, kees@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: arm64: vgic-its: Drop the translation cache reference only for the erased entry Message-ID: References: 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: On Mon, Jun 01, 2026 at 11:53:26PM +0900, Hyunwoo Kim wrote: > vgic_its_invalidate_cache() walks the per-ITS translation cache with > xa_for_each() and drops the cache's reference on each entry with > vgic_put_irq(). It puts the iterated pointer, though, rather than the > value returned by xa_erase(). > > The function is called from contexts that do not exclude one another: the > ITS command handlers hold its_lock, the GITS_CTLR write path holds > cmd_lock, and the path that clears EnableLPIs in a redistributor's > GICR_CTLR holds neither. Two or more of them can drain the same cache > concurrently, and if each one observes the same entry, erases it and then > puts it, the single reference the cache holds on that entry is dropped > more than once. The entry can then be freed while an ITE still maps it. > > xa_erase() is atomic and returns the previous entry, so put only the entry > that this context actually removed. The cache reference is then dropped > exactly once per entry even when the invalidations run concurrently, and > the behavior is unchanged when only one context runs. > > Fixes: 8201d1028caa ("KVM: arm64: vgic-its: Maintain a translation cache per ITS") > Signed-off-by: Hyunwoo Kim Reviewed-by: Oliver Upton Thanks, Oliver > --- > arch/arm64/kvm/vgic/vgic-its.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c > index 1d7e5d560af4..1e3706ac3b8e 100644 > --- a/arch/arm64/kvm/vgic/vgic-its.c > +++ b/arch/arm64/kvm/vgic/vgic-its.c > @@ -597,8 +597,10 @@ static void vgic_its_invalidate_cache(struct vgic_its *its) > unsigned long idx; > > xa_for_each(&its->translation_cache, idx, irq) { > - xa_erase(&its->translation_cache, idx); > - vgic_put_irq(kvm, irq); > + /* Only the context that erases the entry drops its cache ref. */ > + irq = xa_erase(&its->translation_cache, idx); > + if (irq) > + vgic_put_irq(kvm, irq); > } > } > > -- > 2.43.0 >