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 9BAE674E17 for ; Fri, 9 Feb 2024 16:01:40 +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=1707494502; cv=none; b=AY2Unp95Sf3yWdaTIOAGytcf7liSwPeWUdfo8sMpVEueEMdqSRbTwGI6mA7FWeFPCpPMGooRk85EvGC+XB32nluwCC+3qsFvUMCLILXxuPuIq3dx1sSjt+BVBTUHhu7/6vWH8eRZTBjXtX9y5n/TCgEiZ4m8ue4301sRVcFZJQM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707494502; c=relaxed/simple; bh=A0ppvdAEssQ0RgSYaqSvMhcfnozN/meETnSjtqFC/tI=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=c9Bymma5NVttjPCkxeBhNkSYYrNtuCuyer7MPGMQRMHC8ocJeD1xoQ0GD9hw8D/jkhajmtH7nOuZjwCXwqAGYQ1SsjHkg3I99TwI08EMSb++GOXtU8T1KE/m3zeddpTy3ql1tdEvgoyNrW7Zpq9+PAZFK0w6j4kGHqAoRT64v6c= 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=4EplVMy4; 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--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="4EplVMy4" Received: by mail-pg1-f202.google.com with SMTP id 41be03b00d2f7-5cfda2f4716so938741a12.3 for ; Fri, 09 Feb 2024 08:01:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1707494500; x=1708099300; 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=WbkXeYUaDBncgeOsZac9v7h/OYs9uDYhnmPMW2APu84=; b=4EplVMy4iyA5l3qKCK/51jsJKeEElOoEZRUasbbSiG0izQEILpQOILYbxCQzAKKLPc LD1RbJI5dGagCBD4yMfXdUG4O3ObMeVnfKoxoolzEKS5CAPsat2yW1TBqLdRPsViIKHA ez6NA5PGp4106LAXXHcANhSdGE8fPcwpQMCyH/7wzrBRhBXPr1IRveSt+LwahkOKPvgr RzpfGqqZ7GP/Qir5+oeir3f40HP10hFCbkfb3cfCwtIiPZzQEiC8Akqqx5hPceMgFqpd yvDOOIHC5YaGOYJZ/1fclQIOfnq3umsuS/GpBsdchhcmNRW6HT6STIEZ6IxitEX1KyLa qA5A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1707494500; x=1708099300; 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=WbkXeYUaDBncgeOsZac9v7h/OYs9uDYhnmPMW2APu84=; b=h+AXQuiFSmUv8Dg3iMv+z8bOy091D7J7gLxUTeC35kLeTZ5Mn6tuaJGdsZgoQoPaOd DaCyCc2ScqqgntaUmf0SZvRqh+95VEDMljJMZtkGvm0zk4qJDzDNocQqBBEbJd2wIdC+ JtGJg2177F2/iWQV0pZoTfocEGg8gTeR6ch/k2VJ2o5iViCVLrOYNOtrT7VdkoCsK7Bt fio58eGWkMRG9PQwDYJO1GZncqnz+zs/yka//4WvBQ/lB5FrR9rx4DMzTabzEKPOiKK9 tJG3Jv7rw/92bvsnGfsXLTJbb1B6Ir6IZ7aANxbDfnQUCEYNnImSAsMpMCbcSzizJ2Xz qQhw== X-Gm-Message-State: AOJu0YyW+DluL8pApks1nQngnVPs+IUiC8C2dxdlvXWrHvQGDKBv2DY6 liSsi4WD/2IkAaY5UjjX7NOnP2me8flQiArR5BVtf1eD74eXsy48yzo6kjMt7FFUjG4JRkwxYHV A9w== X-Google-Smtp-Source: AGHT+IEyKu+Do4l97DjvOFOUv97OY0Nhkddwujr8IqjGCIn2IxgeG40+kn6W+CdStGVDgL7zUYgHlJTuOeI= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a65:6e8e:0:b0:5d8:cd91:44e4 with SMTP id bm14-20020a656e8e000000b005d8cd9144e4mr5426pgb.12.1707494499773; Fri, 09 Feb 2024 08:01:39 -0800 (PST) Date: Fri, 9 Feb 2024 08:01:38 -0800 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240115125707.1183-1-paul@xen.org> <20240115125707.1183-12-paul@xen.org> <92918ee8-3cc9-41c3-a284-5cd6648abc05@xen.org> <148d903c-fcc5-4a6a-aef1-c1e77e74d0fc@xen.org> Message-ID: Subject: Re: [PATCH v12 11/20] KVM: xen: allow shared_info to be mapped by fixed HVA From: Sean Christopherson To: David Woodhouse Cc: paul@xen.org, Paolo Bonzini , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Shuah Khan , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Thu, Feb 08, 2024, David Woodhouse wrote: > Using anything except NULL as the "no value" value doesn't make sense > to me. It violates the principle of least surprise and would be a > really bad API. I'm a-ok with using '0'. My only request is to check for "!hva" as opposed to "hva == 0", both because that's preferred kernel style, and because it better conveys that it's really checking for !NULL as opposed to address '0'. Side topic, I think the code will end up in a more readable state if the GFN vs. HVA sub-commands are handled in separate case statements, especially if/when xen_lock goes away. E.g. something like this: case KVM_XEN_ATTR_TYPE_SHARED_INFO: { int idx; if (data->u.shared_info.gfn == KVM_XEN_INVALID_GFN) { kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache); r = 0; break; } idx = srcu_read_lock(&kvm->srcu); r = kvm_gpc_activate(&kvm->arch.xen.shinfo_cache, gfn_to_gpa(data->u.shared_info.gfn), PAGE_SIZE); if (!r && kvm->arch.xen.shinfo_cache.active) r = kvm_xen_shared_info_init(kvm); srcu_read_unlock(&kvm->srcu, idx); break; } case KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA: { unsigned long hva = data->u.shared_info.hva; if (hva != untagged_addr(hva) || !access_ok((void __user *)hva) || !PAGE_ALIGNED(hva)) { r = -EINVAL; break; } if (!hva) { kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache); r = 0; break; } r = kvm_gpc_activate_hva(&kvm->arch.xen.shinfo_cache, hva, PAGE_SIZE); if (!r && kvm->arch.xen.shinfo_cache.active) r = kvm_xen_shared_info_init(kvm); break; } Side topic #2, the above requires that __kvm_gpc_refresh() not grab kvm_memslots() in the "using an hva" path, but I think that'd actually be a good thing as it would make it a bit more clear that using an hva bypasses memslots by design.