From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f202.google.com (mail-pg1-f202.google.com [209.85.215.202]) (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 AFFED1FBCB0 for ; Wed, 30 Jul 2025 21:11:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753909885; cv=none; b=pAE2AYP7eVtV7U/4B91Mlop6EVvS3lb3rl2avW1SFDjmE9p4noQGicJ8EEDuY+FVkX9j6tRo+No2vJVJexxRDYUo61b/fC9JWKObqJEyITpfxIX3nsEUpmnrD/CFoAhA0xmR3B6vN5+oxA8FBaeZDh/zQEMLmHECN8SSGNcysG0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753909885; c=relaxed/simple; bh=cVmFzsj3OpZTUi6FUzCWejRWJRm0o5ncvOdXgEoC+OE=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=ReUV5EJVsiVDcTKFfNKqjL9w5OzcRaZnoegzyGmWzA4HAQyNkhTFFtqN/3HI79HbrsfBNd+Et9BJ9Nqxzd5rz3tGjb9gKwayMhwQlOFMU87NLb6RHeJH/cj79LS9PaudgoF9pCrm2h5svAcEygtKPMEUQNPZrPt8AEhME8+ABGg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--jthoughton.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=v2ehqj2B; arc=none smtp.client-ip=209.85.215.202 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--jthoughton.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="v2ehqj2B" Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-b421892319cso149095a12.1 for ; Wed, 30 Jul 2025 14:11:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1753909882; x=1754514682; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=Zcr0HAZVJL/wPM68//kB0QFOkcy4cqNgVvPP1uhkVrY=; b=v2ehqj2B8kahSbPAjtrhq5Gx5GsOrGx4NGAKgBnFM3FtBEeVNMzmrReJ1SZiUBwo4b BjzMoWUFhUCet1vUOyls2ea5sfZP2KAjHxx9jsd6bdsEbFbtCxNTcvCoH72E47N6lO1s kpUyDc9TvCit4qnrUg7hY2ApCIoYSII+OJUx/W52Y3wlKKTAJGgLSH7ovOjNWcjKIjU7 rrJrxI4BheB3UzExcRZlYFCrzrNHyYlsaKSMtK/mupgD7Txg27UTsd0wbb1yikRd0F1K lHTPkXuey0ZNeqFquA1YjUmyJTEQLiSfmR0gW0cvUUNWVHQdSmPAYymdZYWbxdk0MP8W E+Mg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1753909882; x=1754514682; h=content-transfer-encoding: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=Zcr0HAZVJL/wPM68//kB0QFOkcy4cqNgVvPP1uhkVrY=; b=FgId6N/6EPx0rO2OuQN7PywZcVBsdbI1p1de5fWJ7uD4GeMb0IRKcn/op8xtdJwEc6 djqFXK+jg2vXzgY1Dh5jZiojk0SeDDYX6MYOMPO1rllnBhUBBTDPqj5uTlKKSb4oDGGZ 6QWEOZGqiVnb0hPR2WldpONbP+DJOodWsxCW/1RfLzz7PhxlCm1CkUpHvQNRcIGnl2Nw lpoBRGrlmb+Z5jRiPngLBeSgi2Buh0LPYyV6CTsr9U/GccBWAf7BS4KmgLymZKFdfZGH DImoD8uYElm2EX/7AQgFBkjNrEAwlAxnELICuOQZu/Eo2y0XuYE5L2hljsXBHD667mb3 T72Q== X-Forwarded-Encrypted: i=1; AJvYcCX8q8bCOlPWM6iTLSD7+30fFjkPZ040Cs44gEWziR/5GP9pp+fjUkrEhQo+QdrUd5GTmNM=@vger.kernel.org X-Gm-Message-State: AOJu0Yx1SToLPp2WdtpXAbXSqoMMK5BSgtP1gSyhBI0avIZdY8N8QHQ7 FRdRwLP/vS2zoemr2qsL7pCz2nntKkLbaSk1WuOeUfEOUYdJ63imF/W0grxHLrpUQNKOGJVzbJk d5fz8DbWlRH6oGjUn9+3JRQ== X-Google-Smtp-Source: AGHT+IH81SELHZh+GPX7YKucdrOrQjsD2qC5Y2tfTvaMHB5OVH1Y4cxqU+ojrj5t1POmR4E8onsMP+EV8Hr7rDZV X-Received: from pgmb10.prod.google.com ([2002:a63:1b4a:0:b0:b3b:d2a0:df40]) (user=jthoughton job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:12d3:b0:234:216b:cf98 with SMTP id adf61e73a8af0-23dc0e8609fmr7392654637.35.1753909881916; Wed, 30 Jul 2025 14:11:21 -0700 (PDT) Date: Wed, 30 Jul 2025 21:11:18 +0000 In-Reply-To: <20250618042424.330664-6-jthoughton@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250618042424.330664-6-jthoughton@google.com> X-Mailer: git-send-email 2.50.1.565.gc32cd1483b-goog Message-ID: <20250730211120.4163536-1-jthoughton@google.com> Subject: Re: [PATCH v3 05/15] KVM: x86: Add support for KVM userfault exits From: James Houghton To: jthoughton@google.com Cc: amoorthy@google.com, corbet@lwn.net, dmatlack@google.com, kalyazin@amazon.com, kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, maz@kernel.org, oliver.upton@linux.dev, pbonzini@redhat.com, peterx@redhat.com, pgonda@google.com, seanjc@google.com, wei.w.wang@intel.com, yan.y.zhao@intel.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, Jun 17, 2025 at 9:24=E2=80=AFPM James Houghton wrote: > > Only a few changes are needed to support KVM userfault exits on x86: > > 1. Adjust kvm_mmu_hugepage_adjust() to force pages to be mapped at 4K > =C2=A0 =C2=A0while KVM_MEM_USERFAULT is enabled. > 2. Return -EFAULT when kvm_do_userfault() when it reports that the page > =C2=A0 =C2=A0is userfault. (Upon failure to read from the bitmap, > =C2=A0 =C2=A0kvm_do_userfault() will return true without setting up a mem= ory fault > =C2=A0 =C2=A0exit, so we'll return a bare -EFAULT). > > For hugepage recovery, the behavior when disabling KVM_MEM_USERFAULT > should match the behavior when disabling KVM_MEM_LOG_DIRTY_PAGES; make > changes to kvm_mmu_slot_apply_flags() to recover hugepages when > KVM_MEM_USERFAULT is disabled. > > Signed-off-by: James Houghton > Signed-off-by: Sean Christopherson This patch fails to remove the WARN in recover_huge_pages_range(). The diff below will be applied to the next version of this patch, whenever it comes. This WARN can be hit by enabling KVM_MEM_LOG_DIRTY_PAGES and KVM_MEM_USERFAULT, then disabling KVM_MEM_USERFAULT. I've been having offline discussions with Sean about this series; I'm waiting for him to rework the KVM_GENERIC_PAGE_FAULT bits. I'll dedicate some more time to the QEMU side of things too. Thanks. diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 7f3d7229b2c1f..2d83ddb233a9a 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -1779,7 +1779,7 @@ static void recover_huge_pages_range(struct kvm *kvm, u64 huge_spte; int r; =20 - if (WARN_ON_ONCE(kvm_slot_dirty_track_enabled(slot))) + if (kvm_slot_dirty_track_enabled(slot)) return; =20 rcu_read_lock();