Re: [Xen-devel] [PATCH v5 04/14] x86/rtc: replace paravirt rtc check with platform legacy quirk

From: Juergen Gross
Date: Mon Apr 11 2016 - 02:50:32 EST

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On 09/04/16 01:40, Luis R. Rodriguez wrote:
> We have 4 types of x86 platforms that disable RTC:
>
> * Intel MID
> * Lguest - uses paravirt
> * Xen dom-U - uses paravirt
> * x86 on legacy systems annotated with an ACPI legacy flag
>
> We can consolidate all of these into a platform specific legacy
> quirk set early in boot through i386_start_kernel() and through
> x86_64_start_reservations(). This deals with the RTC quirks which
> we can rely on through the hardware subarch, the ACPI check can
> be dealt with separately.
>
> For Xen things are bit more complex given that the @X86_SUBARCH_XEN
> x86_hardware_subarch is shared on for Xen which uses the PV path for
> both domU and dom0. Since the semantics for differentiating between
> the two are Xen specific we provide a platform helper to help override
> default legacy features -- x86_platform.set_legacy_features(). Use
> of this helper is highly discouraged, its only purpose should be
> to account for the lack of semantics available within your given
> x86_hardware_subarch.
>
> As per 0-day, this bumps the vmlinux size using i386-tinyconfig as
> follows:
>
> TOTAL TEXT init.text x86_early_init_platform_quirks()
> +70 +62 +62 +43
>
> Only 8 bytes overhead total, as the main increase in size is
> all removed via __init.

I think this could be even less (see comment below).

>
> v2: split the subarch check from the ACPI check, clarify
> on the ACPI change commit log why ordering works
> v3: add x86_platform.set_legacy_features() to account for dom0,
> add also size impact on vmlinux as per 0-day report

You missed the v5 changes here.

>
> Suggested-by: Ingo Molnar <mingo@xxxxxxxxxx>
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
> ---
> arch/x86/Makefile | 1 +
> arch/x86/include/asm/paravirt.h | 6 ------
> arch/x86/include/asm/paravirt_types.h | 5 -----
> arch/x86/include/asm/processor.h | 1 -
> arch/x86/include/asm/x86_init.h | 21 +++++++++++++++++++++
> arch/x86/kernel/Makefile | 6 +++++-
> arch/x86/kernel/head32.c | 2 ++
> arch/x86/kernel/head64.c | 1 +
> arch/x86/kernel/platform-quirks.c | 21 +++++++++++++++++++++
> arch/x86/kernel/rtc.c | 7 ++-----
> arch/x86/lguest/boot.c | 1 -
> arch/x86/xen/enlighten.c | 10 +++++++---
> 12 files changed, 60 insertions(+), 22 deletions(-)
> create mode 100644 arch/x86/kernel/platform-quirks.c
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 4086abca0b32..f9ed8a7ce2b6 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -209,6 +209,7 @@ endif
> head-y := arch/x86/kernel/head_$(BITS).o
> head-y += arch/x86/kernel/head$(BITS).o
> head-y += arch/x86/kernel/head.o
> +head-y += arch/x86/kernel/platform-quirks.o
>
> libs-y += arch/x86/lib/
>
> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> index 601f1b8f9961..6c7a4a192032 100644
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -20,12 +20,6 @@ static inline int paravirt_enabled(void)
> return pv_info.paravirt_enabled;
> }
>
> -static inline int paravirt_has_feature(unsigned int feature)
> -{
> - WARN_ON_ONCE(!pv_info.paravirt_enabled);
> - return (pv_info.features & feature);
> -}
> -
> static inline void load_sp0(struct tss_struct *tss,
> struct thread_struct *thread)
> {
> diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
> index e8c2326478c8..6acc1b26cf40 100644
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -70,14 +70,9 @@ struct pv_info {
> #endif
>
> int paravirt_enabled;
> - unsigned int features; /* valid only if paravirt_enabled is set */
> const char *name;
> };
>
> -#define paravirt_has(x) paravirt_has_feature(PV_SUPPORTED_##x)
> -/* Supported features */
> -#define PV_SUPPORTED_RTC (1<<0)
> -
> struct pv_init_ops {
> /*
> * Patch may replace one of the defined code sequences with
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 9264476f3d57..0c70c7daa6b8 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -474,7 +474,6 @@ static inline unsigned long current_top_of_stack(void)
> #else
> #define __cpuid native_cpuid
> #define paravirt_enabled() 0
> -#define paravirt_has(x) 0
>
> static inline void load_sp0(struct tss_struct *tss,
> struct thread_struct *thread)
> diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
> index 1ae89a2721d6..8bb8c1a4615a 100644
> --- a/arch/x86/include/asm/x86_init.h
> +++ b/arch/x86/include/asm/x86_init.h
> @@ -142,6 +142,15 @@ struct x86_cpuinit_ops {
> struct timespec;
>
> /**
> + * struct x86_legacy_features - legacy x86 features
> + *
> + * @rtc: this device has a CMOS real-time clock present
> + */
> +struct x86_legacy_features {
> + int rtc;
> +};
> +
> +/**
> * struct x86_platform_ops - platform specific runtime functions
> * @calibrate_tsc: calibrate TSC
> * @get_wallclock: get time from HW clock like RTC etc.
> @@ -152,6 +161,14 @@ struct timespec;
> * @save_sched_clock_state: save state for sched_clock() on suspend
> * @restore_sched_clock_state: restore state for sched_clock() on resume
> * @apic_post_init: adjust apic if neeeded
> + * @legacy: legacy features
> + * @set_legacy_features: override legacy features. Use of this callback
> + * is highly discouraged. You should only need
> + * this if your hardware platform requires further
> + * custom fine tuning far beyong what may be
> + * possible in x86_early_init_platform_quirks() by
> + * only using the current x86_hardware_subarch
> + * semantics.
> */
> struct x86_platform_ops {
> unsigned long (*calibrate_tsc)(void);
> @@ -165,6 +182,8 @@ struct x86_platform_ops {
> void (*save_sched_clock_state)(void);
> void (*restore_sched_clock_state)(void);
> void (*apic_post_init)(void);
> + struct x86_legacy_features legacy;
> + void (*set_legacy_features)(void);
> };
>
> struct pci_dev;
> @@ -186,6 +205,8 @@ extern struct x86_cpuinit_ops x86_cpuinit;
> extern struct x86_platform_ops x86_platform;
> extern struct x86_msi_ops x86_msi;
> extern struct x86_io_apic_ops x86_io_apic_ops;
> +
> +extern void x86_early_init_platform_quirks(void);
> extern void x86_init_noop(void);
> extern void x86_init_uint_noop(unsigned int unused);
>
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 89f8ade0bc7c..7a9e44d935de 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -2,7 +2,11 @@
> # Makefile for the linux kernel.
> #
>
> -extra-y := head_$(BITS).o head$(BITS).o head.o vmlinux.lds
> +extra-y := head_$(BITS).o
> +extra-y += head$(BITS).o
> +extra-y += head.o
> +extra-y += platform-quirks.o
> +extra-y += vmlinux.lds
>
> CPPFLAGS_vmlinux.lds += -U$(UTS_MACHINE)
>
> diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
> index 2911ef3a9f1c..d784bb547a9d 100644
> --- a/arch/x86/kernel/head32.c
> +++ b/arch/x86/kernel/head32.c
> @@ -34,6 +34,8 @@ asmlinkage __visible void __init i386_start_kernel(void)
> cr4_init_shadow();
> sanitize_boot_params(&boot_params);
>
> + x86_early_init_platform_quirks();
> +
> /* Call the subarch specific early setup function */
> switch (boot_params.hdr.hardware_subarch) {
> case X86_SUBARCH_INTEL_MID:
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 1f4422d5c8d0..b72fb0b71dd1 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -182,6 +182,7 @@ void __init x86_64_start_reservations(char *real_mode_data)
> if (!boot_params.hdr.version)
> copy_bootdata(__va(real_mode_data));
>
> + x86_early_init_platform_quirks();
> reserve_ebda_region();
>
> switch (boot_params.hdr.hardware_subarch) {
> diff --git a/arch/x86/kernel/platform-quirks.c b/arch/x86/kernel/platform-quirks.c
> new file mode 100644
> index 000000000000..021a5f973ce3
> --- /dev/null
> +++ b/arch/x86/kernel/platform-quirks.c
> @@ -0,0 +1,21 @@
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +
> +#include <asm/setup.h>
> +#include <asm/bios_ebda.h>
> +
> +void __init x86_early_init_platform_quirks(void)
> +{
> + x86_platform.legacy.rtc = 1;
> +
> + switch (boot_params.hdr.hardware_subarch) {
> + case X86_SUBARCH_XEN:
> + case X86_SUBARCH_LGUEST:
> + case X86_SUBARCH_INTEL_MID:
> + x86_platform.legacy.rtc = 0;
> + break;
> + }
> +
> + if (x86_platform.set_legacy_features)
> + x86_platform.set_legacy_features();
> +}
> diff --git a/arch/x86/kernel/rtc.c b/arch/x86/kernel/rtc.c
> index 4af8d063fb36..62c48da3889d 100644
> --- a/arch/x86/kernel/rtc.c
> +++ b/arch/x86/kernel/rtc.c
> @@ -14,6 +14,7 @@
> #include <asm/time.h>
> #include <asm/intel-mid.h>
> #include <asm/rtc.h>
> +#include <asm/setup.h>
>
> #ifdef CONFIG_X86_32
> /*
> @@ -188,10 +189,6 @@ static __init int add_rtc_cmos(void)
> if (of_have_populated_dt())
> return 0;
>
> - /* Intel MID platforms don't have ioport rtc */
> - if (intel_mid_identify_cpu())
> - return -ENODEV;
> -
> #ifdef CONFIG_ACPI
> if (acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) {
> /* This warning can likely go away again in a year or two. */
> @@ -200,7 +197,7 @@ static __init int add_rtc_cmos(void)
> }
> #endif
>
> - if (paravirt_enabled() && !paravirt_has(RTC))
> + if (!x86_platform.legacy.rtc)
> return -ENODEV;
>
> platform_device_register(&rtc_device);
> diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
> index fd57d3ae7e16..f5497ee5fd2f 100644
> --- a/arch/x86/lguest/boot.c
> +++ b/arch/x86/lguest/boot.c
> @@ -1414,7 +1414,6 @@ __init void lguest_init(void)
> pv_info.kernel_rpl = 1;
> /* Everyone except Xen runs with this set. */
> pv_info.shared_kernel_pmd = 1;
> - pv_info.features = 0;
>
> /*
> * We set up all the lguest overrides for sensitive operations. These
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index 40487f1ecb4c..e066fcf87c3d 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1192,7 +1192,6 @@ static const struct pv_info xen_info __initconst = {
> #ifdef CONFIG_X86_64
> .extra_user_64bit_cs = FLAT_USER_CS64,
> #endif
> - .features = 0,
> .name = "Xen",
> };
>
> @@ -1505,6 +1504,11 @@ static void __init xen_pvh_early_guest_init(void)
> }
> #endif /* CONFIG_XEN_PVH */
>
> +static void xen_dom0_set_legacy_features(void)

Can't you make this __init ?

> +{
> + x86_platform.legacy.rtc = 1;
> +}
> +
> /* First C function to be called on Xen boot */
> asmlinkage __visible void __init xen_start_kernel(void)
> {
> @@ -1525,8 +1529,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
>
> /* Install Xen paravirt ops */
> pv_info = xen_info;
> - if (xen_initial_domain())
> - pv_info.features |= PV_SUPPORTED_RTC;
> pv_init_ops = xen_init_ops;
> if (!xen_pvh_domain()) {
> pv_cpu_ops = xen_cpu_ops;
> @@ -1679,6 +1681,8 @@ asmlinkage __visible void __init xen_start_kernel(void)
> .u.firmware_info.type = XEN_FW_KBD_SHIFT_FLAGS,
> };
>
> + x86_platform.set_legacy_features =
> + xen_dom0_set_legacy_features;
> xen_init_vga(info, xen_start_info->console.dom0.info_size);
> xen_start_info->console.domU.mfn = 0;
> xen_start_info->console.domU.evtchn = 0;
>

Juergen

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