| Message ID | 1455887316-9223-2-git-send-email-mcgrof@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 19/02/16 14:08, Luis R. Rodriguez wrote: > Although hardware_subarch has been in place since the x86 boot > protocol 2.07 it hasn't been used much. Enumerate current possible > values to avoid misuses and help with semantics later at boot > time should this be used further. > > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> > Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org> > --- > arch/x86/include/uapi/asm/bootparam.h | 32 +++++++++++++++++++++++++++++++- > 1 file changed, 31 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h > index 329254373479..dbfb9406436b 100644 > --- a/arch/x86/include/uapi/asm/bootparam.h > +++ b/arch/x86/include/uapi/asm/bootparam.h > @@ -157,7 +157,37 @@ struct boot_params { > __u8 _pad9[276]; /* 0xeec */ > } __attribute__((packed)); > > -enum { > +/** > + * enum x86_hardware_subarch - x86 hardware subarchitecture > + * > + * The x86 hardware_subarch and hardware_subarch_data were added as of the x86 > + * boot protocol 2.07 to help distinguish and supports custom x86 boot > + * sequences. This enum represents accepted values for the x86 > + * hardware_subarch. Custom x86 boot sequences (not X86_SUBARCH_PC) do not have > + * or simply do not make use of natural stubs like BIOS or EFI, the > + * hardware_subarch can be used on the Linux entry path to revector to a > + * subarchitecture stub when needed. This subarchitecture stub can be used to > + * set up Linux boot parameters or for special care to account for nonstandard > + * handling of page tables. > + * > + * KVM and Xen HVM do not have a subarch as these are expected to follow > + * standard x86 boot entries. If there is a genuine need for "hypervisor" type > + * that should be considered separately in the future. > + * > + * @X86_SUBARCH_PC: Should be used if the hardware is enumerable using standard > + * PC mechanisms (PCI, ACPI) and doesn't need a special boot flow. > + * @X86_SUBARCH_LGUEST: Used for x86 hypervisor demo, lguest > + * @X86_SUBARCH_LGUEST: Used for x86 hypervisor demo, lguest Double line > + * @X86_SUBARCH_XEN: Used for Xen guest types which follow the PV boot path, > + * which start at asm startup_xen() entry point and later jump to the C > + * xen_start_kernel() entry point. > + * @X86_SUBARCH_INTEL_MID: Used for Intel MID (Mobile nternet Device) platform s/nternet/Internet/ > + * systems which do not have the PCI legacy interfaces. > + * @X86_SUBARCH_CE4100: Used for Intel CE media processor (CE4100) SOC for > + * for settop boxes and media devices, the use of a subarch for CE4100 > + * is more of a hack... > + */ > +enum x86_hardware_subarch { > X86_SUBARCH_PC = 0, > X86_SUBARCH_LGUEST, > X86_SUBARCH_XEN, > Juergen
On 19/02/16 13:08, Luis R. Rodriguez wrote: > Although hardware_subarch has been in place since the x86 boot > protocol 2.07 it hasn't been used much. Enumerate current possible > values to avoid misuses and help with semantics later at boot > time should this be used further. > > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> > Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org> > --- > arch/x86/include/uapi/asm/bootparam.h | 32 +++++++++++++++++++++++++++++++- > 1 file changed, 31 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h > index 329254373479..dbfb9406436b 100644 > --- a/arch/x86/include/uapi/asm/bootparam.h > +++ b/arch/x86/include/uapi/asm/bootparam.h > @@ -157,7 +157,37 @@ struct boot_params { > __u8 _pad9[276]; /* 0xeec */ > } __attribute__((packed)); > > -enum { > +/** > + * enum x86_hardware_subarch - x86 hardware subarchitecture > + * > + * The x86 hardware_subarch and hardware_subarch_data were added as of the x86 > + * boot protocol 2.07 to help distinguish and supports custom x86 boot > + * sequences. This enum represents accepted values for the x86 > + * hardware_subarch. Custom x86 boot sequences (not X86_SUBARCH_PC) do not have > + * or simply do not make use of natural stubs like BIOS or EFI, the > + * hardware_subarch can be used on the Linux entry path to revector to a > + * subarchitecture stub when needed. This subarchitecture stub can be used to > + * set up Linux boot parameters or for special care to account for nonstandard > + * handling of page tables. This documentation reads like a plan for future implementation. Is this the level of documentation that is needed here? Also, "revector to a subarchitecture stub" is a rather odd way of saying "call a subarch-specific stub". David
On Fri, Feb 19, 2016 at 01:40:33PM +0000, David Vrabel wrote: > On 19/02/16 13:08, Luis R. Rodriguez wrote: > > Although hardware_subarch has been in place since the x86 boot > > protocol 2.07 it hasn't been used much. Enumerate current possible > > values to avoid misuses and help with semantics later at boot > > time should this be used further. > > > > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> > > Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org> > > --- > > arch/x86/include/uapi/asm/bootparam.h | 32 +++++++++++++++++++++++++++++++- > > 1 file changed, 31 insertions(+), 1 deletion(-) > > > > diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h > > index 329254373479..dbfb9406436b 100644 > > --- a/arch/x86/include/uapi/asm/bootparam.h > > +++ b/arch/x86/include/uapi/asm/bootparam.h > > @@ -157,7 +157,37 @@ struct boot_params { > > __u8 _pad9[276]; /* 0xeec */ > > } __attribute__((packed)); > > > > -enum { > > +/** > > + * enum x86_hardware_subarch - x86 hardware subarchitecture > > + * > > + * The x86 hardware_subarch and hardware_subarch_data were added as of the x86 > > + * boot protocol 2.07 to help distinguish and supports custom x86 boot > > + * sequences. This enum represents accepted values for the x86 > > + * hardware_subarch. Custom x86 boot sequences (not X86_SUBARCH_PC) do not have > > + * or simply do not make use of natural stubs like BIOS or EFI, the > > + * hardware_subarch can be used on the Linux entry path to revector to a > > + * subarchitecture stub when needed. This subarchitecture stub can be used to > > + * set up Linux boot parameters or for special care to account for nonstandard > > + * handling of page tables. > > This documentation reads like a plan for future implementation. Is this > the level of documentation that is needed here? > > Also, "revector to a subarchitecture stub" is a rather odd way of saying > "call a subarch-specific stub". I took feedback directly from hpa's replies about what the subarch is from my original linker table series. So its not me concocting this. It also shows how your own lack of clarify on this isn't doing us any good either, and its precisely why I am documenting this now. The lack of semantics here has gotten us intro trouble as it is not allowing us to tool in proactive solutions to prevent bugs. My goal is first to clarify some definitions, and then use them and tool them to proactiveley avoid bugs. Luis
diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h index 329254373479..dbfb9406436b 100644 --- a/arch/x86/include/uapi/asm/bootparam.h +++ b/arch/x86/include/uapi/asm/bootparam.h @@ -157,7 +157,37 @@ struct boot_params { __u8 _pad9[276]; /* 0xeec */ } __attribute__((packed)); -enum { +/** + * enum x86_hardware_subarch - x86 hardware subarchitecture + * + * The x86 hardware_subarch and hardware_subarch_data were added as of the x86 + * boot protocol 2.07 to help distinguish and supports custom x86 boot + * sequences. This enum represents accepted values for the x86 + * hardware_subarch. Custom x86 boot sequences (not X86_SUBARCH_PC) do not have + * or simply do not make use of natural stubs like BIOS or EFI, the + * hardware_subarch can be used on the Linux entry path to revector to a + * subarchitecture stub when needed. This subarchitecture stub can be used to + * set up Linux boot parameters or for special care to account for nonstandard + * handling of page tables. + * + * KVM and Xen HVM do not have a subarch as these are expected to follow + * standard x86 boot entries. If there is a genuine need for "hypervisor" type + * that should be considered separately in the future. + * + * @X86_SUBARCH_PC: Should be used if the hardware is enumerable using standard + * PC mechanisms (PCI, ACPI) and doesn't need a special boot flow. + * @X86_SUBARCH_LGUEST: Used for x86 hypervisor demo, lguest + * @X86_SUBARCH_LGUEST: Used for x86 hypervisor demo, lguest + * @X86_SUBARCH_XEN: Used for Xen guest types which follow the PV boot path, + * which start at asm startup_xen() entry point and later jump to the C + * xen_start_kernel() entry point. + * @X86_SUBARCH_INTEL_MID: Used for Intel MID (Mobile nternet Device) platform + * systems which do not have the PCI legacy interfaces. + * @X86_SUBARCH_CE4100: Used for Intel CE media processor (CE4100) SOC for + * for settop boxes and media devices, the use of a subarch for CE4100 + * is more of a hack... + */ +enum x86_hardware_subarch { X86_SUBARCH_PC = 0, X86_SUBARCH_LGUEST, X86_SUBARCH_XEN,
Although hardware_subarch has been in place since the x86 boot protocol 2.07 it hasn't been used much. Enumerate current possible values to avoid misuses and help with semantics later at boot time should this be used further. Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org> --- arch/x86/include/uapi/asm/bootparam.h | 32 +++++++++++++++++++++++++++++++- 1 file changed, 31 insertions(+), 1 deletion(-)