From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34319) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WSnPX-00015w-5v for qemu-devel@nongnu.org; Wed, 26 Mar 2014 08:58:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WSnPR-0004n7-0G for qemu-devel@nongnu.org; Wed, 26 Mar 2014 08:58:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34531) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WSnPQ-0004mz-OO for qemu-devel@nongnu.org; Wed, 26 Mar 2014 08:58:20 -0400 Date: Wed, 26 Mar 2014 14:58:28 +0200 From: "Michael S. Tsirkin" Message-ID: <20140326125828.GA2192@redhat.com> References: <20140326064510.5518.72436.malonedeb@chaenomeles.canonical.com> <20140326064510.5518.72436.malonedeb@chaenomeles.canonical.com> <20140326103112.GA20219@redhat.com> <5332C7D2.3030901@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <5332C7D2.3030901@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [Bug 1297651] [NEW] KVM create a win7 guest with Qemu, it boots up fail List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Laszlo Ersek Cc: robert.hu@intel.com, qemu-devel@nongnu.org, ehabkost@redhat.com, Bug 1297651 <1297651@bugs.launchpad.net> On Wed, Mar 26, 2014 at 01:28:02PM +0100, Laszlo Ersek wrote: > On 03/26/14 11:31, Michael S. Tsirkin wrote: >=20 > > On Wed, Mar 26, 2014 at 06:45:10AM -0000, Robert Hu wrote: >=20 > >> Date: Mon Mar 17 17:05:16 2014 +0100 > >> > >> i386/acpi-build: allow more than 255 elements in CPON > >> > >> The build_ssdt() function builds a number of AML objects that ar= e related > >> to CPU hotplug, and whose IDs form a contiguous sequence of APIC= IDs. > >> (APIC IDs are in fact discontiguous, but this is the traditional > >> interface: build a contiguous sequence from zero up that covers = all > >> possible APIC IDs.) These objects are: > >> > >> - a Processor() object for each VCPU, > >> - a NTFY method, with one branch for each VCPU, > >> - a CPON package with one element (hotplug status byte) for each= VCPU. > >> > >> The build_ssdt() function currently limits the *count* of proces= sor > >> objects, and NTFY branches, and CPON elements, in 0xFF (see the = assignment > >> to "acpi_cpus"). This allows for an inclusive APIC ID range of [= 0..254]. > >> This is incorrect, because the highest APIC ID that we otherwise= allow a > >> VCPU to take is 255. > >> > >> In order to extend the maximum count to 256, and the traversed A= PIC ID > >> range correspondingly to [0..255]: > >> - the Processor() objects need no change, > >> - the NTFY method also needs no change, > >> - the CPON package must be updated, because it is defined with a > >> DefPackage, and the number of elements in such a package can b= e at most > >> 255. We pick a DefVarPackage instead. > >> > >> We replace the Op byte, and the encoding of the number of elemen= ts. > >> Compare: > >> > >> DefPackage :=3D PackageOp PkgLength NumElements Packag= eElementList > >> DefVarPackage :=3D VarPackageOp PkgLength VarNumElements Packag= eElementList > >> > >> PackageOp :=3D 0x12 > >> VarPackageOp :=3D 0x13 > >=20 > >=20 > > I think I know what's going on here: the specification says: > >=20 > > The ASL compiler can emit two different AML opcodes for a Package > > declaration, either PackageOp or VarPackageOp. For small, fixed-lengt= h > > packages, the PackageOp is used and this > >=20 > > opcode is compatible with ACPI 1.0. A VarPackageOp will be emitted if > > any of the following conditions are true: > > =E2=80=A2 > > The NumElements argument is a TermArg that can only be resolved at > > runtime. > > =E2=80=A2 > > At compile time, NumElements resolves to a constant that is larger t= han > > 255. > > =E2=80=A2 > > The PackageList contains more than 255 initializer elements. > >=20 > >=20 > > So we clearly violate this rule. >=20 > I did see this passage of the spec, but it is not relevant. It is about= what the ASL compiler does. It comes from: >=20 > 19 ACPI Source Language (ASL)Reference > 19.5 ASL Operator Reference > 19.5.98 Package (Declare Package Object) >=20 > We do not have an ASL compiler at hand. True. But I think the spec and guests simply didn't envision writing AML = by hand :) > The specification nowhere restricts VarPackageOp to > 255. >=20 > However, what I *did* mess up is compatibility with ACPI 1.0. Just belo= w the quoted part, there's also this: >=20 > Note: The ability to create variable-sized packages was first > introduced in ACPI 2.0. ACPI 1.0 only allowed fixed-size > packages with up to 255 elements. >=20 > I forgot that the header of the containing table stated the ACPI versio= n: >=20 > /* Copy header and patch values in the S3_ / S4_ / S5_ packages */ > ssdt_ptr =3D acpi_data_push(table_data, sizeof(ssdp_misc_aml)); >=20 > and >=20 > DefinitionBlock ("ssdt-misc.aml", "SSDT", 0x01, "BXPC", "BXSSDTSUSP"= , 0x1) > ^^^^ > ComplianceRevision >=20 > So my patch generates ACPI 2.0+ contents for an 1.0 table. >=20 > > The following seems to fix the issue - still testing. Can you confirm= please? >=20 > This patch only restricts the bug to a subset of cases, but it doesn't = fix it. >=20 > > However the question we should ask is whether > > it's a good idea to allow hotplug ID values that might > > make guests fail to boot. > >=20 > > How about limiting ACPI_CPU_HOTPLUG_ID_LIMIT to 255? >=20 > I think it's not the package size / APIC ID value per se that breaks th= e boot, but the incompatibility between the ACPI revision stated in the S= SDT header, and the construct in the table. It would be interesting to try tweaking the table version and seeing what happens. Does it help any guests? > >=20 > > We never allowed > 255 in the past, is it worth the > > maintainance headaches? > >=20 > > =20 > > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c > > index f1054dd..7597517 100644 > > --- a/hw/i386/acpi-build.c > > +++ b/hw/i386/acpi-build.c > > @@ -1055,9 +1055,21 @@ build_ssdt(GArray *table_data, GArray *linker, > > =20 > > { > > GArray *package =3D build_alloc_array(); > > - uint8_t op =3D 0x13; /* VarPackageOp */ > > + uint8_t op; > > + > > + /* > > + * Note: The ability to create variable-sized packages w= as first introduced in ACPI 2.0. ACPI 1.0 only > > + * allowed fixed-size packages with up to 255 elements. > > + * Windows guests up to win2k8 fail when VarPackageOp is= used. > > + */ > > + if (acpi_cpus <=3D 255) { > > + op =3D 0x12; /* PackageOp */ > > + build_append_byte(package, acpi_cpus); /* NumElement= s */ > > + } else { > > + op =3D 0x13; /* VarPackageOp */ > > + build_append_int(package, acpi_cpus); /* VarNumEleme= nts */ > > + } > > =20 > > - build_append_int(package, acpi_cpus); /* VarNumElements = */ > > for (i =3D 0; i < acpi_cpus; i++) { > > uint8_t b =3D test_bit(i, cpu->found_cpus) ? 0x01 : = 0x00; > > build_append_byte(package, b); > >=20 >=20 > The patch will mask the problem for most of the cases, but when VarPack= ageOp is used, it will be broken just the same (because the ACPI revision= in the SSDT header will still mismatch). yes but modern guests don't seem to care, and it was already broken in 1.7, wasn't it? > Here's my proposal: > - I can post a patch that changes the SSDT DSL files, *and* the DSDT fi= les (q35-acpi-dsdt.dsl acpi-dsdt.dsl), to state an ACPI revision of 2.0. = (The ACPI revision of the DSDT file determines integer sizes for SSDTs to= o, so we can't just bump the SSDTs to 2.0) It should not be a problem but I'm not sure I get this comment. Can you e= xplain? > - Or I suggest to revert my patches for 2.0. >=20 > You probably won't like bumping the ACPI rev in DSDT/SSDT, for various = compatibility reasons, so I think I suggest to revert these two patches o= f mine. It's now clear to me that this VCPU hotplug limit cannot be lifte= d without much more intrusive (and guest visible) changes. Sorry about mi= ssing this fact in my original submission. >=20 > Thanks, > Laszlo I have a problem with both approaches :) If we want to change ACPI rev, I think we should do this conditionally when max_cpus > 255. Would be worth it if this fixes some guests. As for reverting, I think it's a problem that we seem to allow max_cpus =3D 256 but then it doesn't really work. I think the patch I posted might be good enough for 2.0. It seems to make things work for new guests, and old guests work as long as you don't specify max_cpus =3D 255. The config with a high max_cpus value never really worked so not a big deal. Alternatively limit max_cpus to 255, to make it fail cleanly. --=20 MST