Received: from eggs.gnu.org ([2001:4830:134:3::10]:59220) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gYw3D-0001rG-SW for qemu-devel@nongnu.org; Mon, 17 Dec 2018 11:47:29 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gYw3C-0004Nm-Nd for qemu-devel@nongnu.org; Mon, 17 Dec 2018 11:47:27 -0500 Date: Mon, 17 Dec 2018 17:46:48 +0100 From: Samuel Ortiz Message-ID: <20181217164648.GG4456@caravaggio> References: <20181217104838.18957-1-sameo@linux.intel.com> <20181217104838.18957-8-sameo@linux.intel.com> <20181217132028.4e387d2d@Igors-MacBook-Pro.local> <20181217134959.GB4456@caravaggio> <20181217163536.034fd13c@Igors-MacBook-Pro.local> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20181217163536.034fd13c@Igors-MacBook-Pro.local> Subject: Re: [Qemu-devel] [PATCH v4 7/8] hw: acpi: Export and share the ARM RSDP build List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov Cc: Laurent Vivier , Peter Maydell , Thomas Huth , Eduardo Habkost , Ben Warren , "Michael S. Tsirkin" , qemu-devel@nongnu.org, Shannon Zhao , qemu-arm@nongnu.org, Paolo Bonzini , Richard Henderson On Mon, Dec 17, 2018 at 04:35:36PM +0100, Igor Mammedov wrote: > On Mon, 17 Dec 2018 14:49:59 +0100 > Samuel Ortiz wrote: > > > On Mon, Dec 17, 2018 at 01:20:28PM +0100, Igor Mammedov wrote: > > > On Mon, 17 Dec 2018 11:48:37 +0100 > > > Samuel Ortiz wrote: > > > > > > > Now that build_rsdp() supports building both legacy and current RSDP > > > > tables, we can move it to a generic folder (hw/acpi) and have the i386 > > > > ACPI code reuse it in order to reduce code duplication. > > > > > > > > Signed-off-by: Samuel Ortiz > > > > Reviewed-by: Philippe Mathieu-Daudé > > > > Tested-by: Philippe Mathieu-Daudé > > > > Reviewed-by: Andrew Jones > > > > Reviewed-by: Igor Mammedov > > > for future reference, if one changes patch in a significant way, > > > one is supposed to drop Tested/Reviewed-by tags so that reviewers > > > would look at it again and we by mistake won't merge not actually > > > reviewed changes. > > > > > > [...] > > > > > > > diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c > > > > index fb877648ac..846cb6d755 100644 > > > > --- a/hw/i386/acpi-build.c > > > > +++ b/hw/i386/acpi-build.c > > > > @@ -2547,35 +2547,6 @@ build_amd_iommu(GArray *table_data, BIOSLinker *linker) > > > > "IVRS", table_data->len - iommu_start, 1, NULL, NULL); > > > > } > > > > > > > > -static void > > > > -build_rsdp(GArray *rsdp_table, BIOSLinker *linker, unsigned rsdt_tbl_offset) > > > > -{ > > > > - /* AcpiRsdpDescriptor describes revision 2 RSDP table and as result we > > > > - * allocate extra 16 bytes for pc/q35 RSDP rev1 as well. Keep extra 16 bytes > > > > - * wasted to make sure we won't breake migration for machine types older > > > > - * than 2.3 due to size mismatch. > > > > - */ > > > > - AcpiRsdpDescriptor *rsdp = acpi_data_push(rsdp_table, sizeof *rsdp); > > > > - unsigned rsdt_pa_size = sizeof(rsdp->rsdt_physical_address); > > > > - unsigned rsdt_pa_offset = > > > > - (char *)&rsdp->rsdt_physical_address - rsdp_table->data; > > > > - > > > > - bios_linker_loader_alloc(linker, ACPI_BUILD_RSDP_FILE, rsdp_table, 16, > > > > - true /* fseg memory */); > > > > - > > > > - memcpy(&rsdp->signature, "RSD PTR ", 8); > > > > - memcpy(rsdp->oem_id, ACPI_BUILD_APPNAME6, 6); > > > > - /* Address to be filled by Guest linker */ > > > > - bios_linker_loader_add_pointer(linker, > > > > - ACPI_BUILD_RSDP_FILE, rsdt_pa_offset, rsdt_pa_size, > > > > - ACPI_BUILD_TABLE_FILE, rsdt_tbl_offset); > > > > - > > > > - /* Checksum to be filled by Guest linker */ > > > > - bios_linker_loader_add_checksum(linker, ACPI_BUILD_RSDP_FILE, > > > > - (char *)rsdp - rsdp_table->data, 20 /* ACPI rev 1.0 RSDP size */, > > > > - (char *)&rsdp->checksum - rsdp_table->data); > > > > -} > > > > - > > > > typedef > > > > struct AcpiBuildState { > > > > /* Copy of table in RAM (for patching). */ > > > > @@ -2732,7 +2703,25 @@ void acpi_build(AcpiBuildTables *tables, MachineState *machine) > > > > slic_oem.id, slic_oem.table_id); > > > > > > > > /* RSDP is in FSEG memory, so allocate it separately */ > > > > - build_rsdp(tables->rsdp, tables->linker, rsdt); > > > > + { > > > > + AcpiRsdpData rsdp_data = { > > > > + .revision = 0, > > > > + .oem_id = ACPI_BUILD_APPNAME6, > > > > + .xsdt_tbl_offset = NULL, > > > > + .rsdt_tbl_offset = &rsdt, > > > > + }; > > > > + build_rsdp(tables->rsdp, tables->linker, &rsdp_data); > > > > + if (!pcmc->rsdp_in_ram) { > > > > + /* > > > > + * Legacy machine types (2.2 and older) expect to get a complete > > > > + * revision 2 RSDP table, even though they only look at the > > > not true, rev is set to 0 for pc machines, > > Rev is set to 0 but they effectively expect to get a structure which > > size is the rev 2 one. That's what I meant. > > > > > the point of the original comment was > > > that we allocate extra 16 bytes but not actually using them and why it's bad > > > to drop it suddenly. > > > > > > > + * revision 0 fields (xsdt pointer is not set). So in order to > > > > + * not break migration to those machine types we waste 16 bytes > > > > + * that we amend to the RSDP revision 0 structure. > > > ^^^ added > > > > + */ > > > Perhaps amended original comment would be clearer: > > > > > > /* We used to allocate extra space for RSDP rev 2 but used only space for > > > * legacy RSDP and extra bytes were zeroed out. Keep wasting extra 16 bytes > > > * to make sure we won't breake migration for machine types 2.2 and older > > > * due to RSDP blob size mismatch. > > > */ > > > > > > > + build_append_int_noprefix(tables->rsdp, 0, 16); > Looks like I've haven't noticed, it might work but are you sure? > 0 here is uint64_t and then it's shifted 16 times which is sort of gray area (undefined behavior) AFAIK shifting by N bits when N > width(left operand) is undefined but that's not the case here. build_append_int_noprefix(foo, 0, 16) shift a 64 bits wide unsigned int by 8 bits, for each iterations of a 16 iterations loop. So we're doing 16 iterations of properly defined behaviour. Cheers, Samuel.