Received-SPF: pass (google.com: domain of linux-kernel+bounces-70698-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Subject: Re: [PATCH v4 4/6] LoongArch: Add paravirt interface for guest kernel
To: Huacai Chen <chenhuacai@kernel.org>
Cc: Tianrui Zhao <zhaotianrui@loongson.cn>, Juergen Gross <jgross@suse.com>,
 Paolo Bonzini <pbonzini@redhat.com>, loongarch@lists.linux.dev,
 linux-kernel@vger.kernel.org, virtualization@lists.linux.dev,
 kvm@vger.kernel.org
References: <20240201031950.3225626-1-maobibo@loongson.cn>
 <20240201031950.3225626-5-maobibo@loongson.cn>
 <CAAhV-H7dXsU+WM172PWi_m8TYpYmzG_SW-vVQcdnOdETUxQ9+w@mail.gmail.com>
From: maobibo <maobibo@loongson.cn>
Message-ID: <63f8bd29-c0da-167b-187d-61c56eb081a6@loongson.cn>
Date: Mon, 19 Feb 2024 12:11:52 +0800
User-Agent: Mozilla/5.0 (X11; Linux loongarch64; rv:68.0) Gecko/20100101
 Thunderbird/68.7.0
Precedence: bulk
MIME-Version: 1.0
In-Reply-To: <CAAhV-H7dXsU+WM172PWi_m8TYpYmzG_SW-vVQcdnOdETUxQ9+w@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 8bit


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@loongson.cn> 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@loongson.cn>
>> ---
>>   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;
}

>> +
>> +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?

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