Re: [SeaBIOS] [Qemu-devel] Commit 77af8a2b95b79699de650965d5228772743efe84 breaks Windows 2000 support

[Phil Dennis-Jordan]

Thanks for this, Paolo. Very interesting idea.

I couldn't get things working initially, but with a few fixups on the
SeaBIOS side I can boot both legacy and modern OSes. See comments
inline below for details on changes required.

Successfully booted (only a brief test):
- Windows 2000
- Windows XP (32 bit)
- Windows 7 (32 bit)
- Windows 10 (64 bit, SeaBIOS)
- Windows 10 (64 bit, OVMF)
- macOS 10.12 (patched OVMF)

On Tue, Jul 25, 2017 at 7:10 PM, Paolo Bonzini  wrote:
> On 25/07/2017 18:23, Paolo Bonzini wrote:
> > On 25/07/2017 18:14, Laszlo Ersek wrote:
> > > "No regressions became apparent in tests with a range of Windows
> > >    (XP-10)"
> > >
> > > In theory, w2k falls within that range.
> >
> > Nope, Windows 2000 is like NT 5.0, XP is like NT 5.1. :(
> >
> > One possibility is to fix it in SeaBIOS instead: if you get a 2.0 FADT
> > and an XSDT and no RSDT, it can build an RSDT and a 1.0 FADT itself,
> > patching the RSDT to point to it.
> >
> > It's a hack, but it's the only place I see to make it "just work".  And
> > it could be extended nicely in the future.
> >
> > All QEMU would have to do is to provide an XSDT _instead_ of an RSDT.
>
> Completely untested code follows.  Machine type compatibility code
> should not be necessary because new QEMU always starts with a new BIOS.
>
> Not sure I'll have much time for this in the next few days, so help
> is appreciated.
>
> Paolo
>
> QEMU:
>
> diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
> index 36a6cc450e..ea750d54d9 100644
> --- a/hw/acpi/aml-build.c
> +++ b/hw/acpi/aml-build.c
> @@ -1573,33 +1573,6 @@ void acpi_build_tables_cleanup(AcpiBuildTables *tables, bool mfre)
>      g_array_free(tables->vmgenid, mfre);
>  }
>
> -/* Build rsdt table */
> -void
> -build_rsdt(GArray *table_data, BIOSLinker *linker, GArray *table_offsets,
>       const char *oem_id, const char *oem_table_id)
>
> -{
> int i;
> unsigned rsdt_entries_offset;
> AcpiRsdtDescriptorRev1 *rsdt;
> const unsigned table_data_len = (sizeof(uint32_t) * table_offsets->len);
> const unsigned rsdt_entry_size = sizeof(rsdt->table_offset_entry[0]);
> const size_t rsdt_len = sizeof(*rsdt) + table_data_len;
> rsdt = acpi_data_push(table_data, rsdt_len);
> rsdt_entries_offset = (char *)rsdt->table_offset_entry - table_data->data;
> for (i = 0; i < table_offsets->len; ++i) {
>    uint32_t ref_tbl_offset = g_array_index(table_offsets, uint32_t, i);
>    uint32_t rsdt_entry_offset = rsdt_entries_offset + rsdt_entry_size * i;
>    /* rsdt->table_offset_entry to be filled by Guest linker */
>    bios_linker_loader_add_pointer(linker,
>        ACPI_BUILD_TABLE_FILE, rsdt_entry_offset, rsdt_entry_size,
>        ACPI_BUILD_TABLE_FILE, ref_tbl_offset);
> }
> build_header(linker, table_data,
>             (void *)rsdt, "RSDT", rsdt_len, 1, oem_id, oem_table_id);
>
> -}
>
> /* Build xsdt table */
>  void
>  build_xsdt(GArray *table_data, BIOSLinker *linker, GArray *table_offsets,
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index 6b7bade183..ad00f6affd 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -2557,12 +2557,12 @@ build_amd_iommu(GArray *table_data, BIOSLinker *linker)
>  }
>
> static GArray *
> -build_rsdp(GArray *rsdp_table, BIOSLinker *linker, unsigned rsdt_tbl_offset)
> +build_rsdp(GArray *rsdp_table, BIOSLinker *linker, unsigned xsdt_tbl_offset)
>  {
>      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;
>
> unsigned xsdt_pa_size = sizeof(rsdp->xsdt_physical_address);
>
> unsigned xsdt_pa_offset =
>    (char *)&rsdp->xsdt_physical_address - rsdp_table->data;
>
> bios_linker_loader_alloc(linker, ACPI_BUILD_RSDP_FILE, rsdp_table, 16,
>                             true /* fseg memory */);
>
> @@ -2571,8 +2571,8 @@ build_rsdp(GArray *rsdp_table, BIOSLinker *linker, unsigned rsdt_tbl_offset)
>      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);
>    ACPI_BUILD_RSDP_FILE, xsdt_pa_offset, xsdt_pa_size,
>    ACPI_BUILD_TABLE_FILE, xsdt_tbl_offset);
>
> /* Checksum to be filled by Guest linker */
>    bios_linker_loader_add_checksum(linker, ACPI_BUILD_RSDP_FILE,
>
> @@ -2621,7 +2621,7 @@ void acpi_build(AcpiBuildTables *tables, MachineState *machine)
>      PCMachineState *pcms = PC_MACHINE(machine);
>      PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
>      GArray *table_offsets;
> unsigned facs, dsdt, rsdt, fadt;
> unsigned facs, dsdt, xsdt, fadt;
> AcpiPmInfo pm;
> AcpiMiscInfo misc;
> AcpiMcfgInfo mcfg;
>
> @@ -2730,12 +2730,12 @@ void acpi_build(AcpiBuildTables *tables, MachineState *machine)
>      }
>  /* RSDT is pointed to by RSDP */
> rsdt = tables_blob->len;
> build_rsdt(tables_blob, tables->linker, table_offsets,
>
> xsdt = tables_blob->len;
>
> build_xsdt(tables_blob, tables->linker, table_offsets,
>            slic_oem.id, slic_oem.table_id);
>
> /* RSDP is in FSEG memory, so allocate it separately */
> build_rsdp(tables->rsdp, tables->linker, rsdt);
>
> build_rsdp(tables->rsdp, tables->linker, xsdt);
>
> /* We'll expose it all to Guest so we want to reduce
> chance of size changes.
>
> SeaBIOS:
>
> From 73b0facdb7349f5dbf24dc675647b68eeeec0ff4 Mon Sep 17 00:00:00 2001
> From: Paolo Bonzini 
> Date: Tue, 25 Jul 2017 18:50:19 +0200
> Subject: [PATCH 1/2] seabios: build RSDT from XSDT
>
> Old operating systems would like to have a v1 FADT, but new
> operating systems would like to have v3.
>
> Since old operating systems do not know about XSDTs, the
> solution is to point the RSDT to a v1 FADT and the XSDT to a
> v3 FADT.
>
> But, OVMF is not able to do that and barfs when it sees the
> second FADT---plus really it's only BIOS operating systems
> such as win2k that complain.  So instead: 1) make QEMU provide
> an XSDT only; 2) build the RSDT and v1 FADT in SeaBIOS.
>
> This patch makes SeaBIOS build an RSDT out of an existing XSDT.
> Signed-off-by: Paolo Bonzini
>
> src/fw/paravirt.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
>  src/std/acpi.h    | 11 +++++++++++
>  2 files changed, 55 insertions(+), 1 deletion(-)
>
> diff --git a/src/fw/paravirt.c b/src/fw/paravirt.c
> index 5b23d78..19a4abe 100644
> --- a/src/fw/paravirt.c
> +++ b/src/fw/paravirt.c
> @@ -25,6 +25,7 @@
>  #include "x86.h" // cpuid
>  #include "xen.h" // xen_biostable_setup
>  #include "stacks.h" // yield
> +#include "std/acpi.h"
>
> // Amount of continuous ram under 4Gig
>  u32 RamSize;
> @@ -147,6 +148,46 @@ static void msr_feature_control_setup(void)
>          wrmsr_smp(MSR_IA32_FEATURE_CONTROL, feature_control_bits);
>  }
>
> +static void
> +build_compatibility_rsdt(void)
> +{
> if (RsdpAddr->rsdt_physical_address)
>    return;
> u64 xsdt_addr = RsdpAddr->xsdt_physical_address;
> if (xsdt_addr & ~0xffffffffULL)
>    return;
> struct xsdt_descriptor_rev1 *xsdt = (void*)(u32)xsdt_addr;
> void *end = (void*)xsdt + xsdt->length;
> struct rsdt_descriptor_rev1 *rsdt;
> int rsdt_size = offsetof(struct rsdt_descriptor_rev1, table_offset_entry[0]);
> int i;
> for (i=0; (void*)&xsdt->table_offset_entry[i] < end; i++) {
>    u64 tbl_addr = xsdt->table_offset_entry[i];
>    if (!tbl_addr || (tbl_addr & ~0xffffffffULL))
>        continue;
>    rsdt_size += 4;
> }
> rsdt = malloc_high(rsdt_size);
> RsdpAddr->rsdt_physical_address = (u32)rsdt;

Modifying the RSDP like this invalidates both its checksums, so they
need to be adjusted. Something like this:

RsdpAddr->checksum -= checksum(RsdpAddr, offsetof(struct
rsdp_descriptor, length));
    RsdpAddr->extended_checksum -= checksum(RsdpAddr, sizeof(struct
rsdp_descriptor));
> memcpy(rsdt, xsdt, sizeof(struct acpi_table_header));
> rsdt->signature = RSDT_SIGNATURE;
> rsdt->length = rsdt_size;
> rsdt->revision = 1;
> int j;
> for (i=j=0; (void*)&xsdt->table_offset_entry[i] < end; i++) {
>    u64 tbl_addr = xsdt->table_offset_entry[i];
>    if (!tbl_addr || (tbl_addr & ~0xffffffffULL))
>        continue;
>    rsdt->table_offset_entry[j++] = (u32)tbl_addr;
> }
> rsdt->checksum -= checksum(rsdt, rsdt_size);
>
> +}
>
> void
>  qemu_platform_setup(void)
>  {
> @@ -186,8 +227,10 @@ qemu_platform_setup(void)
>      RsdpAddr = find_acpi_rsdp();
>
>    if (RsdpAddr)
>    if (RsdpAddr) {
>        build_compatibility_rsdt();
>        return;
>    }
>
>    /* If present, loader should have installed an RSDP.
>     * Not installed? We might still be able to continue
>
> diff --git a/src/std/acpi.h b/src/std/acpi.h
> index c2ea707..caf5e7e 100644
> --- a/src/std/acpi.h
> +++ b/src/std/acpi.h
> @@ -133,6 +133,17 @@ struct rsdt_descriptor_rev1
>  } PACKED;
>
> /*
> ACPI 2.0 Root System Description Table (RSDT)
> */

Comment should be "ACPI 2.0 Extended System Description Table (XSDT)"
> +#define XSDT_SIGNATURE 0x54445358 // RSDT

The signature is "XSDT", that works out to 0x58445358
> +struct xsdt_descriptor_rev1
> +{
> ACPI_TABLE_HEADER_DEF       /* ACPI common table header */
> u64 table_offset_entry[0];  /* Array of pointers to other */
> /* ACPI tables */
>
> +} PACKED;
>
> +/*
> ACPI 1.0 Firmware ACPI Control Structure (FACS)
>
> */
> #define FACS_SIGNATURE 0x53434146 // FACS
>
> 2.13.3
>
> From 46c7a296d27bd487cfd89a40973b1e61426dfbd0 Mon Sep 17 00:00:00 2001
> From: Paolo Bonzini 
> Date: Tue, 25 Jul 2017 18:59:20 +0200
> Subject: [PATCH 2/2] seabios: create v1 FADT in compatibility RSDT
>
> This patch presents a v1 FADT inside the compatibility RSDT, so
> that old operating systems are not broken.
> Signed-off-by: Paolo Bonzini
>
> src/fw/paravirt.c | 18 +++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/src/fw/paravirt.c b/src/fw/paravirt.c
> index 19a4abe..a9b9e80 100644
> --- a/src/fw/paravirt.c
> +++ b/src/fw/paravirt.c
> @@ -148,6 +148,18 @@ static void msr_feature_control_setup(void)
>          wrmsr_smp(MSR_IA32_FEATURE_CONTROL, feature_control_bits);
>  }
>
> +static void*
> +build_rev1_fadt(struct fadt_descriptor_rev1 *fadt_v3)
> +{
> struct fadt_descriptor_rev1 *fadt_v1 = malloc_high(sizeof *fadt_v1);
> memcpy(fadt_v1, fadt_v3, sizeof *fadt_v1);
> fadt_v1->length = sizeof *fadt_v1;
> fadt_v1->revision = 1;

We should mask out the flags bits that are reserved in ACPI 1.0 as
they refer to fields not present in this revision's FADT. e.g.

// upper 23 bits reserved in rev1 FADT
    fadt_v1->flags &= 0x1ff;
> fadt_v1->checksum -= checksum(fadt_v1, fadt_v1->length);
> return fadt_v1;
>
> +}
>
> static void
>  build_compatibility_rsdt(void)
>  {
> @@ -182,6 +194,12 @@ build_compatibility_rsdt(void)
>          u64 tbl_addr = xsdt->table_offset_entry[i];
>          if (!tbl_addr || (tbl_addr & ~0xffffffffULL))
>              continue;
>    struct acpi_table_header *tbl = (void*)(u32)tbl_addr;
>    /* The RSDT should only have an ACPI 1.0 FADT according to
>     * the spec.
>     */
>    if (tbl->signature == FACP_SIGNATURE && tbl->revision > 1)
>        tbl_addr = (u32)build_rev1_fadt((void *)tbl);
>    rsdt->table_offset_entry[j++] = (u32)tbl_addr;
> }

With these changes:

Reviewed-by: Phil Dennis-Jordan