From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (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 AB8262248AD for ; Fri, 10 Jan 2025 22:34:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736548448; cv=none; b=GKjbkExxTZEYYRTTaOSVmREHVhJ7ngTzrg5W+y3+tesX/VmEGAru2sx4Mh2hh3dsLoScfutjpZeSVgvb3KwdlyZNl80sgx5o/eV/x00ifxwlOsQOcahwQlKHnfJNIVFKH4gYggohbnAJF021x7qN0/d+t+vX0+qn1gTQv1uJPqs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736548448; c=relaxed/simple; bh=QhXWiFicIHGyIb+atPjAutlwdLtBYGpec+stYRCczYY=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=JLFb17AMnwfK1/4/Bxzaloe6UK7hduYTJnqjwX77MuOyiexz/A2d1tsStx9bqUOGagomqtve8R5BqimVt69Ee0WGEalACQwxm+mmHr9alOfoWHBBhuXl6ECMBSrCauPKm+2Q4VA1Avgk53pTLAv53OY3bTP9FqP5tdPnjhSnle0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=RU4uyQVp; arc=none smtp.client-ip=209.85.216.73 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--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="RU4uyQVp" Received: by mail-pj1-f73.google.com with SMTP id 98e67ed59e1d1-2ef775ec883so4513787a91.1 for ; Fri, 10 Jan 2025 14:34:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1736548446; x=1737153246; darn=vger.kernel.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=toPMy/p1FGPMloT0sAIUsexrUKcnNTRt9KQgn0hs/FI=; b=RU4uyQVpKyXRuQeCkEkvEeF3ILJE/Jm7gD/o2HmCTQBJ3ZTvHEZK4AF8UHZS1VMtdE wbeBPq6JfPqrXrcBU9YzuRReJO7EImkeO5f87QGN2e4O2yXYa7L/Cu1AzyQW0Zz2dwz6 OkSJGDaBQiqSrQio3/vGs1vtw4YfIekLkBeS+3KZkr3NRGH3leghzbS+r3MIfCiI3H+H uIR/LKSNgvC1tKGcBvmAX314w2D3muYwwbBawnh8hxEKpjIOnZEIp8QmdpykQ6kgiMiC NGYvR5IC/PBUkm2IBbqcA/BkJUoFSgGLif0moxUUgqoAbvSSkHheMlqfsDgIyARJf7N8 rzDA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1736548446; x=1737153246; 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=toPMy/p1FGPMloT0sAIUsexrUKcnNTRt9KQgn0hs/FI=; b=GSaK8SuTswFGShkvZFncEc4Qn8eEALRRf98FZ4wVG3n5mPuFXl8pWCUE14JcGqfOJX ZFKWcHfcmxvJnrFx9Ddf2o2s4OzzjB3GnsfXMe3o5rlkfMJmPWumhzXHgPnJAac3eSLE QbuS1zKoAaFGw4CCh9v+15cV5nGJuqRuv4aC6SXSysZVQCpdKrtwFlw7zIm1l3RRuSrN oaX6DWLMvmulGk3b6J1YATnSNJTSyuwmxKI1IEVm34hqv5fwwR2nwzQOk7An7Qd24+8r ZoLGhuwi/BEeOStZgZL98c5IwWZjERQ4F/TdbAhyWsTV4xkeEpvh74hE3TqvTeApQkin 5VUw== X-Forwarded-Encrypted: i=1; AJvYcCWmEWVGKqe2gj10TgjWI+VHLje5Cf/keLBqQxOqN5mJ4HclgeS6j+H4V0yYngcVWypwUEI=@vger.kernel.org X-Gm-Message-State: AOJu0YzqnkB29XR02QJctZ4LxrG00+X7VNrzqVXrlxN46dh8JJwbbDzb KzlAjqfgv2+eUZzhWaK/ZkWv0bj5DgdUmPtEXx3KfS0JHwZlKUSmNGrnTTVAPLJn4TBgQZs7z3+ ZnA== X-Google-Smtp-Source: AGHT+IEk2Z2gcbkycWhUhHC/lVeYrgSkArCCD2IOK/WGv6zeS0D9LDXtvPqkULftwsZBr7LJiZeXo3F7qnw= X-Received: from pfbcm15.prod.google.com ([2002:a05:6a00:338f:b0:728:e508:8a3e]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:a8f:b0:72a:ae66:3050 with SMTP id d2e1a72fcca58-72d21f31510mr14154004b3a.1.1736548446042; Fri, 10 Jan 2025 14:34:06 -0800 (PST) Date: Fri, 10 Jan 2025 14:34:04 -0800 In-Reply-To: <20241105184333.2305744-4-jthoughton@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20241105184333.2305744-1-jthoughton@google.com> <20241105184333.2305744-4-jthoughton@google.com> Message-ID: Subject: Re: [PATCH v8 03/11] KVM: x86/mmu: Factor out spte atomic bit clearing routine From: Sean Christopherson To: James Houghton Cc: Paolo Bonzini , David Matlack , David Rientjes , Marc Zyngier , Oliver Upton , Wei Xu , Yu Zhao , Axel Rasmussen , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Tue, Nov 05, 2024, James Houghton wrote: > This new function, tdp_mmu_clear_spte_bits_atomic(), will be used in a > follow-up patch to enable lockless Accessed and R/W/X bit clearing. This is a lie. tdp_mmu_clear_spte_bits_atomic() can only be used to clear the Accessed bit, clearing RWX bits for access-tracked SPTEs *must* be done with a CMPXCHG so that the original RWX protections are preserved. > Signed-off-by: James Houghton > --- > arch/x86/kvm/mmu/tdp_iter.h | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kvm/mmu/tdp_iter.h b/arch/x86/kvm/mmu/tdp_iter.h > index 2880fd392e0c..a24fca3f9e7f 100644 > --- a/arch/x86/kvm/mmu/tdp_iter.h > +++ b/arch/x86/kvm/mmu/tdp_iter.h > @@ -25,6 +25,13 @@ static inline u64 kvm_tdp_mmu_write_spte_atomic(tdp_ptep_t sptep, u64 new_spte) > return xchg(rcu_dereference(sptep), new_spte); > } > > +static inline u64 tdp_mmu_clear_spte_bits_atomic(tdp_ptep_t sptep, u64 mask) > +{ > + atomic64_t *sptep_atomic = (atomic64_t *)rcu_dereference(sptep); > + > + return (u64)atomic64_fetch_and(~mask, sptep_atomic); > +} > + > static inline void __kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 new_spte) > { > KVM_MMU_WARN_ON(is_ept_ve_possible(new_spte)); > @@ -63,12 +70,8 @@ static inline u64 kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 old_spte, > static inline u64 tdp_mmu_clear_spte_bits(tdp_ptep_t sptep, u64 old_spte, > u64 mask, int level) > { > - atomic64_t *sptep_atomic; > - > - if (kvm_tdp_mmu_spte_need_atomic_write(old_spte, level)) { > - sptep_atomic = (atomic64_t *)rcu_dereference(sptep); > - return (u64)atomic64_fetch_and(~mask, sptep_atomic); > - } > + if (kvm_tdp_mmu_spte_need_atomic_write(old_spte, level)) > + return tdp_mmu_clear_spte_bits_atomic(sptep, mask); > > __kvm_tdp_mmu_write_spte(sptep, old_spte & ~mask); > return old_spte; > -- > 2.47.0.199.ga7371fff76-goog >