Re: [PATCH v4 4/6] LoongArch: Add paravirt interface for guest kernel

[Huacai Chen]

On Mon, Feb 19, 2024 at 5:21 PM maobibo <maobibo@xxxxxxxxxxx> wrote:
>
>
>
> On 2024/2/19 下午4:48, Huacai Chen wrote:
> > On Mon, Feb 19, 2024 at 12:11 PM maobibo <maobibo@xxxxxxxxxxx> wrote:
> >>
> >>
> >>
> >> On 2024/2/19 上午10:42, Huacai Chen wrote:
> >>> Hi, Bibo,
> >>>
> >>> On Thu, Feb 1, 2024 at 11:19 AM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
> >>>>
> >>>> The patch adds paravirt interface for guest kernel, function
> >>>> pv_guest_initi() firstly checks whether system runs on VM mode. If kernel
> >>>> runs on VM mode, it will call function kvm_para_available() to detect
> >>>> whether current VMM is KVM hypervisor. And the paravirt function can work
> >>>> only if current VMM is KVM hypervisor, since there is only KVM hypervisor
> >>>> supported on LoongArch now.
> >>>>
> >>>> This patch only adds paravirt interface for guest kernel, however there
> >>>> is not effective pv functions added here.
> >>>>
> >>>> Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
> >>>> ---
> >>>>    arch/loongarch/Kconfig                        |  9 ++++
> >>>>    arch/loongarch/include/asm/kvm_para.h         |  7 ++++
> >>>>    arch/loongarch/include/asm/paravirt.h         | 27 ++++++++++++
> >>>>    .../include/asm/paravirt_api_clock.h          |  1 +
> >>>>    arch/loongarch/kernel/Makefile                |  1 +
> >>>>    arch/loongarch/kernel/paravirt.c              | 41 +++++++++++++++++++
> >>>>    arch/loongarch/kernel/setup.c                 |  2 +
> >>>>    7 files changed, 88 insertions(+)
> >>>>    create mode 100644 arch/loongarch/include/asm/paravirt.h
> >>>>    create mode 100644 arch/loongarch/include/asm/paravirt_api_clock.h
> >>>>    create mode 100644 arch/loongarch/kernel/paravirt.c
> >>>>
> >>>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> >>>> index 10959e6c3583..817a56dff80f 100644
> >>>> --- a/arch/loongarch/Kconfig
> >>>> +++ b/arch/loongarch/Kconfig
> >>>> @@ -585,6 +585,15 @@ config CPU_HAS_PREFETCH
> >>>>           bool
> >>>>           default y
> >>>>
> >>>> +config PARAVIRT
> >>>> +       bool "Enable paravirtualization code"
> >>>> +       depends on AS_HAS_LVZ_EXTENSION
> >>>> +       help
> >>>> +          This changes the kernel so it can modify itself when it is run
> >>>> +         under a hypervisor, potentially improving performance significantly
> >>>> +         over full virtualization.  However, when run without a hypervisor
> >>>> +         the kernel is theoretically slower and slightly larger.
> >>>> +
> >>>>    config ARCH_SUPPORTS_KEXEC
> >>>>           def_bool y
> >>>>
> >>>> diff --git a/arch/loongarch/include/asm/kvm_para.h b/arch/loongarch/include/asm/kvm_para.h
> >>>> index 9425d3b7e486..41200e922a82 100644
> >>>> --- a/arch/loongarch/include/asm/kvm_para.h
> >>>> +++ b/arch/loongarch/include/asm/kvm_para.h
> >>>> @@ -2,6 +2,13 @@
> >>>>    #ifndef _ASM_LOONGARCH_KVM_PARA_H
> >>>>    #define _ASM_LOONGARCH_KVM_PARA_H
> >>>>
> >>>> +/*
> >>>> + * Hypcall code field
> >>>> + */
> >>>> +#define HYPERVISOR_KVM                 1
> >>>> +#define HYPERVISOR_VENDOR_SHIFT                8
> >>>> +#define HYPERCALL_CODE(vendor, code)   ((vendor << HYPERVISOR_VENDOR_SHIFT) + code)
> >>>> +
> >>>>    /*
> >>>>     * LoongArch hypcall return code
> >>>>     */
> >>>> diff --git a/arch/loongarch/include/asm/paravirt.h b/arch/loongarch/include/asm/paravirt.h
> >>>> new file mode 100644
> >>>> index 000000000000..b64813592ba0
> >>>> --- /dev/null
> >>>> +++ b/arch/loongarch/include/asm/paravirt.h
> >>>> @@ -0,0 +1,27 @@
> >>>> +/* SPDX-License-Identifier: GPL-2.0 */
> >>>> +#ifndef _ASM_LOONGARCH_PARAVIRT_H
> >>>> +#define _ASM_LOONGARCH_PARAVIRT_H
> >>>> +
> >>>> +#ifdef CONFIG_PARAVIRT
> >>>> +#include <linux/static_call_types.h>
> >>>> +struct static_key;
> >>>> +extern struct static_key paravirt_steal_enabled;
> >>>> +extern struct static_key paravirt_steal_rq_enabled;
> >>>> +
> >>>> +u64 dummy_steal_clock(int cpu);
> >>>> +DECLARE_STATIC_CALL(pv_steal_clock, dummy_steal_clock);
> >>>> +
> >>>> +static inline u64 paravirt_steal_clock(int cpu)
> >>>> +{
> >>>> +       return static_call(pv_steal_clock)(cpu);
> >>>> +}
> >>> The steal time code can be removed in this patch, I think.
> >>>
> >> Originally I want to remove this piece of code, but it fails to compile
> >> if CONFIG_PARAVIRT is selected. Here is reference code, function
> >> paravirt_steal_clock() must be defined if CONFIG_PARAVIRT is selected.
> >>
> >> static __always_inline u64 steal_account_process_time(u64 maxtime)
> >> {
> >> #ifdef CONFIG_PARAVIRT
> >>           if (static_key_false(&paravirt_steal_enabled)) {
> >>                   u64 steal;
> >>
> >>                   steal = paravirt_steal_clock(smp_processor_id());
> >>                   steal -= this_rq()->prev_steal_time;
> >>                   steal = min(steal, maxtime);
> >>                   account_steal_time(steal);
> >>                   this_rq()->prev_steal_time += steal;
> >>
> >>                   return steal;
> >>           }
> >> #endif
> >>           return 0;
> >> }
> > OK, then keep it.
> >
> >>
> >>>> +
> >>>> +int pv_guest_init(void);
> >>>> +#else
> >>>> +static inline int pv_guest_init(void)
> >>>> +{
> >>>> +       return 0;
> >>>> +}
> >>>> +
> >>>> +#endif // CONFIG_PARAVIRT
> >>>> +#endif
> >>>> diff --git a/arch/loongarch/include/asm/paravirt_api_clock.h b/arch/loongarch/include/asm/paravirt_api_clock.h
> >>>> new file mode 100644
> >>>> index 000000000000..65ac7cee0dad
> >>>> --- /dev/null
> >>>> +++ b/arch/loongarch/include/asm/paravirt_api_clock.h
> >>>> @@ -0,0 +1 @@
> >>>> +#include <asm/paravirt.h>
> >>>> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> >>>> index 3c808c680370..662e6e9de12d 100644
> >>>> --- a/arch/loongarch/kernel/Makefile
> >>>> +++ b/arch/loongarch/kernel/Makefile
> >>>> @@ -48,6 +48,7 @@ obj-$(CONFIG_MODULES)         += module.o module-sections.o
> >>>>    obj-$(CONFIG_STACKTRACE)       += stacktrace.o
> >>>>
> >>>>    obj-$(CONFIG_PROC_FS)          += proc.o
> >>>> +obj-$(CONFIG_PARAVIRT)         += paravirt.o
> >>>>
> >>>>    obj-$(CONFIG_SMP)              += smp.o
> >>>>
> >>>> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
> >>>> new file mode 100644
> >>>> index 000000000000..21d01d05791a
> >>>> --- /dev/null
> >>>> +++ b/arch/loongarch/kernel/paravirt.c
> >>>> @@ -0,0 +1,41 @@
> >>>> +// SPDX-License-Identifier: GPL-2.0
> >>>> +#include <linux/export.h>
> >>>> +#include <linux/types.h>
> >>>> +#include <linux/jump_label.h>
> >>>> +#include <linux/kvm_para.h>
> >>>> +#include <asm/paravirt.h>
> >>>> +#include <linux/static_call.h>
> >>>> +
> >>>> +struct static_key paravirt_steal_enabled;
> >>>> +struct static_key paravirt_steal_rq_enabled;
> >>>> +
> >>>> +static u64 native_steal_clock(int cpu)
> >>>> +{
> >>>> +       return 0;
> >>>> +}
> >>>> +
> >>>> +DEFINE_STATIC_CALL(pv_steal_clock, native_steal_clock);
> >>> The steal time code can be removed in this patch, I think.
> >> Ditto, the same reason with above.
> >>>
> >>>> +
> >>>> +static bool kvm_para_available(void)
> >>>> +{
> >>>> +       static int hypervisor_type;
> >>>> +       int config;
> >>>> +
> >>>> +       if (!hypervisor_type) {
> >>>> +               config = read_cpucfg(CPUCFG_KVM_SIG);
> >>>> +               if (!memcmp(&config, KVM_SIGNATURE, 4))
> >>>> +                       hypervisor_type = HYPERVISOR_KVM;
> >>>> +       }
> >>>> +
> >>>> +       return hypervisor_type == HYPERVISOR_KVM;
> >>>> +}
> >>>> +
> >>>> +int __init pv_guest_init(void)
> >>>> +{
> >>>> +       if (!cpu_has_hypervisor)
> >>>> +               return 0;
> >>>> +       if (!kvm_para_available())
> >>>> +               return 0;
> >>>> +
> >>>> +       return 1;
> >>>> +}
> >>>> diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> >>>> index edf2bba80130..de5c36dccc49 100644
> >>>> --- a/arch/loongarch/kernel/setup.c
> >>>> +++ b/arch/loongarch/kernel/setup.c
> >>>> @@ -43,6 +43,7 @@
> >>>>    #include <asm/efi.h>
> >>>>    #include <asm/loongson.h>
> >>>>    #include <asm/numa.h>
> >>>> +#include <asm/paravirt.h>
> >>>>    #include <asm/pgalloc.h>
> >>>>    #include <asm/sections.h>
> >>>>    #include <asm/setup.h>
> >>>> @@ -367,6 +368,7 @@ void __init platform_init(void)
> >>>>           pr_info("The BIOS Version: %s\n", b_info.bios_version);
> >>>>
> >>>>           efi_runtime_init();
> >>>> +       pv_guest_init();
> >>> I prefer use CONFIG_PARAVIRT here, though you have a dummy version for
> >>> !CONFIG_PARAVIRT, I think it is better to let others clearly know that
> >>> PARAVIRT is an optional feature.
> >> I remember that there is rule that CONFIG_xxx had better be used in
> >> header files rather than c code, so that the code looks neat. Am I wrong?
> > That depends on what we want, sometimes we want to hide the details,
> > but sometimes we want to give others a notice.
> I want to keep code clean here :)
>
> >
> > And there is another problem: if you want to centralize all pv init
> > functions, it is better to use pv_features_init() rather than
> > pv_guest_init(); if you want to give each feature an init function,
> > then we don't need pv_guest_init here, and we can then add a
> > pv_ipi_init() in the last patch.
> Currently I have no idea how to add other pv features like pv
> stealtimer, I will consider this when adding other pv features.
> pv_ipi_init/pv_guest_init is both ok for me, pv_ipi_init is better for now.
Then you want to add an init function for each feature, so please
rename to pv_ipi_init(), move to the last patch and in
loongson_smp_setup().

Huacai

>
> Regards
> Bibo Mao
>
> >
> > Huacai
> >
> >>
> >> Regards
> >> Bibo Mao
> >>>
> >>> Huacai
> >>>
> >>>
> >>> Huacai
> >>>>    }
> >>>>
> >>>>    static void __init check_kernel_sections_mem(void)
> >>>> --
> >>>> 2.39.3
> >>>>
> >>>>
> >>
>