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Subject: Re: [PATCH v20 27/30] LoongArch: KVM: Implement vcpu world switch
To:     WANG Xuerui <kernel@xen0n.name>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Huacai Chen <chenhuacai@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        loongarch@lists.linux.dev, Jens Axboe <axboe@kernel.dk>,
        Mark Brown <broonie@kernel.org>,
        Alex Deucher <alexander.deucher@amd.com>,
        Oliver Upton <oliver.upton@linux.dev>, maobibo@loongson.cn,
        Xi Ruoyao <xry111@xry111.site>
References: <20230831083020.2187109-1-zhaotianrui@loongson.cn>
 <20230831083020.2187109-28-zhaotianrui@loongson.cn>
 <eff83dfe-5f89-6b46-2197-2873ede705bd@xen0n.name>
From:   zhaotianrui <zhaotianrui@loongson.cn>
Message-ID: <8e88d249-f1fd-2024-e1f1-c63e84ef33ec@loongson.cn>
Date:   Tue, 12 Sep 2023 17:55:49 +0800
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在 2023/9/8 上午4:04, WANG Xuerui 写道:
>
> On 8/31/23 16:30, Tianrui Zhao wrote:
>> Implement LoongArch vcpu world switch, including vcpu enter guest and
>> vcpu exit from guest, both operations need to save or restore the host
>> and guest registers.
>>
>> Reviewed-by: Bibo Mao <maobibo@loongson.cn>
>> Signed-off-by: Tianrui Zhao <zhaotianrui@loongson.cn>
>> ---
>>   arch/loongarch/kernel/asm-offsets.c |  32 ++++
>>   arch/loongarch/kvm/switch.S         | 255 ++++++++++++++++++++++++++++
>>   2 files changed, 287 insertions(+)
>>   create mode 100644 arch/loongarch/kvm/switch.S
>>
>> diff --git a/arch/loongarch/kernel/asm-offsets.c 
>> b/arch/loongarch/kernel/asm-offsets.c
>> index 505e4bf596..d4bbaa74c1 100644
>> --- a/arch/loongarch/kernel/asm-offsets.c
>> +++ b/arch/loongarch/kernel/asm-offsets.c
>> @@ -9,6 +9,7 @@
>>   #include <linux/mm.h>
>>   #include <linux/kbuild.h>
>>   #include <linux/suspend.h>
>> +#include <linux/kvm_host.h>
>>   #include <asm/cpu-info.h>
>>   #include <asm/ptrace.h>
>>   #include <asm/processor.h>
>> @@ -285,3 +286,34 @@ void output_fgraph_ret_regs_defines(void)
>>       BLANK();
>>   }
>>   #endif
>> +
>> +static void __used output_kvm_defines(void)
>> +{
>> +    COMMENT(" KVM/LOONGARCH Specific offsets. ");
> "LoongArch"?
Thanks, I will fix it.
>> +
>> +    OFFSET(VCPU_FCSR0, kvm_vcpu_arch, fpu.fcsr);
>> +    OFFSET(VCPU_FCC, kvm_vcpu_arch, fpu.fcc);
>> +    BLANK();
>> +
>> +    OFFSET(KVM_VCPU_ARCH, kvm_vcpu, arch);
>> +    OFFSET(KVM_VCPU_KVM, kvm_vcpu, kvm);
>> +    OFFSET(KVM_VCPU_RUN, kvm_vcpu, run);
>> +    BLANK();
>> +
>> +    OFFSET(KVM_ARCH_HSP, kvm_vcpu_arch, host_sp);
>> +    OFFSET(KVM_ARCH_HTP, kvm_vcpu_arch, host_tp);
>> +    OFFSET(KVM_ARCH_HANDLE_EXIT, kvm_vcpu_arch, handle_exit);
>> +    OFFSET(KVM_ARCH_HPGD, kvm_vcpu_arch, host_pgd);
>> +    OFFSET(KVM_ARCH_GEENTRY, kvm_vcpu_arch, guest_eentry);
>> +    OFFSET(KVM_ARCH_GPC, kvm_vcpu_arch, pc);
>> +    OFFSET(KVM_ARCH_GGPR, kvm_vcpu_arch, gprs);
>> +    OFFSET(KVM_ARCH_HESTAT, kvm_vcpu_arch, host_estat);
>> +    OFFSET(KVM_ARCH_HBADV, kvm_vcpu_arch, badv);
>> +    OFFSET(KVM_ARCH_HBADI, kvm_vcpu_arch, badi);
>> +    OFFSET(KVM_ARCH_HECFG, kvm_vcpu_arch, host_ecfg);
>> +    OFFSET(KVM_ARCH_HEENTRY, kvm_vcpu_arch, host_eentry);
>> +    OFFSET(KVM_ARCH_HPERCPU, kvm_vcpu_arch, host_percpu);
>> +
>> +    OFFSET(KVM_GPGD, kvm, arch.pgd);
>> +    BLANK();
>> +}
>> diff --git a/arch/loongarch/kvm/switch.S b/arch/loongarch/kvm/switch.S
>> new file mode 100644
>> index 0000000000..f637fcd56c
>> --- /dev/null
>> +++ b/arch/loongarch/kvm/switch.S
>> @@ -0,0 +1,255 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * Copyright (C) 2020-2023 Loongson Technology Corporation Limited
>> + */
>> +
>> +#include <linux/linkage.h>
>> +#include <asm/stackframe.h>
>> +#include <asm/asm.h>
>> +#include <asm/asmmacro.h>
>> +#include <asm/regdef.h>
>> +#include <asm/loongarch.h>
>> +
>> +#define PT_GPR_OFFSET(x)    (PT_R0 + 8*x)
>> +#define GGPR_OFFSET(x)        (KVM_ARCH_GGPR + 8*x)
>> +
>> +.macro kvm_save_host_gpr base
>> +    .irp n,1,2,3,22,23,24,25,26,27,28,29,30,31
>> +    st.d    $r\n, \base, PT_GPR_OFFSET(\n)
>> +    .endr
>> +.endm
>> +
>> +.macro kvm_restore_host_gpr base
>> +    .irp n,1,2,3,22,23,24,25,26,27,28,29,30,31
>> +    ld.d    $r\n, \base, PT_GPR_OFFSET(\n)
>> +    .endr
>> +.endm
>> +
>> +/*
>> + * save and restore all gprs except base register,
>> + * and default value of base register is a2.
>> + */
>> +.macro kvm_save_guest_gprs base
>> +    .irp 
>> n,1,2,3,4,5,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31
>> +    st.d    $r\n, \base, GGPR_OFFSET(\n)
>> +    .endr
>> +.endm
>> +
>> +.macro kvm_restore_guest_gprs base
>> +    .irp 
>> n,1,2,3,4,5,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31
>> +    ld.d    $r\n, \base, GGPR_OFFSET(\n)
>> +    .endr
>> +.endm
>> +
>> +/*
>> + * prepare switch to guest, save host reg and restore guest reg.
>> + * a2: kvm_vcpu_arch, don't touch it until 'ertn'
>> + * t0, t1: temp register
>> + */
>> +.macro kvm_switch_to_guest
>> +    /* set host excfg.VS=0, all exceptions share one exception entry */
>> +    csrrd        t0, LOONGARCH_CSR_ECFG
>> +    bstrins.w    t0, zero, CSR_ECFG_VS_SHIFT_END, CSR_ECFG_VS_SHIFT
>> +    csrwr        t0, LOONGARCH_CSR_ECFG
>> +
>> +    /* Load up the new EENTRY */
>> +    ld.d    t0, a2, KVM_ARCH_GEENTRY
>> +    csrwr    t0, LOONGARCH_CSR_EENTRY
>> +
>> +    /* Set Guest ERA */
>> +    ld.d    t0, a2, KVM_ARCH_GPC
>> +    csrwr    t0, LOONGARCH_CSR_ERA
>> +
>> +    /* Save host PGDL */
>> +    csrrd    t0, LOONGARCH_CSR_PGDL
>> +    st.d    t0, a2, KVM_ARCH_HPGD
>> +
>> +    /* Switch to kvm */
>> +    ld.d    t1, a2, KVM_VCPU_KVM - KVM_VCPU_ARCH
>> +
>> +    /* Load guest PGDL */
>> +    li.w    t0, KVM_GPGD
>> +    ldx.d   t0, t1, t0
>> +    csrwr    t0, LOONGARCH_CSR_PGDL
>> +
>> +    /* Mix GID and RID */
>> +    csrrd        t1, LOONGARCH_CSR_GSTAT
>> +    bstrpick.w    t1, t1, CSR_GSTAT_GID_SHIFT_END, CSR_GSTAT_GID_SHIFT
>> +    csrrd        t0, LOONGARCH_CSR_GTLBC
>> +    bstrins.w    t0, t1, CSR_GTLBC_TGID_SHIFT_END, CSR_GTLBC_TGID_SHIFT
>> +    csrwr        t0, LOONGARCH_CSR_GTLBC
>> +
>> +    /*
>> +     * Switch to guest:
>> +     *  GSTAT.PGM = 1, ERRCTL.ISERR = 0, TLBRPRMD.ISTLBR = 0
>> +     *  ertn
>> +     */
>> +
>> +    /*
>> +     * Enable intr in root mode with future ertn so that host interrupt
>> +     * can be responsed during VM runs
>> +     * guest crmd comes from separate gcsr_CRMD register
>> +     */
>> +    ori    t0, zero, CSR_PRMD_PIE
> Use "li.w" like the place several lines before?
Thanks for the advice, and this issue has been discussed before, and the 
conclusion is that it need not replace "ori" with the pseudo instruction 
like "li.w", as it has the same meaning.
>> +    csrxchg    t0, t0, LOONGARCH_CSR_PRMD
>> +
>> +    /* Set PVM bit to setup ertn to guest context */
>> +    ori    t0, zero, CSR_GSTAT_PVM
> Similarly here...
>> +    csrxchg    t0, t0, LOONGARCH_CSR_GSTAT
>> +
>> +    /* Load Guest gprs */
>> +    kvm_restore_guest_gprs a2
>> +    /* Load KVM_ARCH register */
>> +    ld.d    a2, a2,    (KVM_ARCH_GGPR + 8 * REG_A2)
>> +
>> +    ertn
>> +.endm
>> +
>> +    /*
>> +     * exception entry for general exception from guest mode
>> +     *  - IRQ is disabled
>> +     *  - kernel privilege in root mode
>> +     *  - page mode keep unchanged from previous prmd in root mode
>> +     *  - Fixme: tlb exception cannot happen since registers 
>> relative with TLB
>> +     *  -        is still in guest mode, such as pgd table/vmid 
>> registers etc,
>> +     *  -        will fix with hw page walk enabled in future
>> +     * load kvm_vcpu from reserved CSR KVM_VCPU_KS, and save a2 to 
>> KVM_TEMP_KS
>> +     */
>> +    .text
>> +    .cfi_sections    .debug_frame
>> +SYM_CODE_START(kvm_vector_entry)
>> +    csrwr    a2,   KVM_TEMP_KS
>> +    csrrd    a2,   KVM_VCPU_KS
>> +    addi.d    a2,   a2, KVM_VCPU_ARCH
>> +
>> +    /* After save gprs, free to use any gpr */
>> +    kvm_save_guest_gprs a2
>> +    /* Save guest a2 */
>> +    csrrd    t0,    KVM_TEMP_KS
>> +    st.d    t0,    a2,    (KVM_ARCH_GGPR + 8 * REG_A2)
>> +
>> +    /* a2: kvm_vcpu_arch, a1 is free to use */
>> +    csrrd    s1,   KVM_VCPU_KS
>> +    ld.d    s0,   s1, KVM_VCPU_RUN
>> +
>> +    csrrd    t0,   LOONGARCH_CSR_ESTAT
>> +    st.d    t0,   a2, KVM_ARCH_HESTAT
>> +    csrrd    t0,   LOONGARCH_CSR_ERA
>> +    st.d    t0,   a2, KVM_ARCH_GPC
>> +    csrrd    t0,   LOONGARCH_CSR_BADV
>> +    st.d    t0,   a2, KVM_ARCH_HBADV
>> +    csrrd    t0,   LOONGARCH_CSR_BADI
>> +    st.d    t0,   a2, KVM_ARCH_HBADI
>> +
>> +    /* Restore host excfg.VS */
>> +    csrrd    t0, LOONGARCH_CSR_ECFG
>> +    ld.d    t1, a2, KVM_ARCH_HECFG
>> +    or    t0, t0, t1
>> +    csrwr    t0, LOONGARCH_CSR_ECFG
>> +
>> +    /* Restore host eentry */
>> +    ld.d    t0, a2, KVM_ARCH_HEENTRY
>> +    csrwr    t0, LOONGARCH_CSR_EENTRY
>> +
>> +    /* restore host pgd table */
>> +    ld.d    t0, a2, KVM_ARCH_HPGD
>> +    csrwr   t0, LOONGARCH_CSR_PGDL
>> +
>> +    /*
>> +     * Disable PGM bit to enter root mode by default with next ertn
>> +     */
>> +    ori    t0, zero, CSR_GSTAT_PVM
> And here.
>> +    csrxchg    zero, t0, LOONGARCH_CSR_GSTAT
>> +    /*
>> +     * Clear GTLBC.TGID field
>> +     *       0: for root  tlb update in future tlb instr
>> +     *  others: for guest tlb update like gpa to hpa in future tlb 
>> instr
>> +     */
>> +    csrrd    t0, LOONGARCH_CSR_GTLBC
>> +    bstrins.w    t0, zero, CSR_GTLBC_TGID_SHIFT_END, 
>> CSR_GTLBC_TGID_SHIFT
>> +    csrwr    t0, LOONGARCH_CSR_GTLBC
>> +    ld.d    tp, a2, KVM_ARCH_HTP
>> +    ld.d    sp, a2, KVM_ARCH_HSP
>> +    /* restore per cpu register */
>> +    ld.d    u0, a2, KVM_ARCH_HPERCPU
>> +    addi.d    sp, sp, -PT_SIZE
>> +
>> +    /* Prepare handle exception */
>> +    or    a0, s0, zero
>> +    or    a1, s1, zero
> Similarly "move X, Y" should be clearer here.
>> +    ld.d    t8, a2, KVM_ARCH_HANDLE_EXIT
>> +    jirl    ra, t8, 0
>> +
>> +    or    a2, s1, zero
>> +    addi.d    a2, a2, KVM_VCPU_ARCH
>> +
>> +    /* resume host when ret <= 0 */
>> +    bge    zero, a0, ret_to_host
> "blez a0, ret_to_host"
>> +
>> +    /*
>> +         * return to guest
>> +         * save per cpu register again, maybe switched to another cpu
>> +         */
>> +    st.d    u0, a2, KVM_ARCH_HPERCPU
>> +
>> +    /* Save kvm_vcpu to kscratch */
>> +    csrwr    s1, KVM_VCPU_KS
>> +    kvm_switch_to_guest
>> +
>> +ret_to_host:
>> +    ld.d    a2, a2, KVM_ARCH_HSP
>> +    addi.d  a2, a2, -PT_SIZE
>> +    kvm_restore_host_gpr    a2
>> +    jr      ra
>> +
>> +SYM_INNER_LABEL(kvm_vector_entry_end, SYM_L_LOCAL)
>> +SYM_CODE_END(kvm_vector_entry)
>> +
>> +/*
>> + * int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu)
>> + *
>> + * @register_param:
>> + *  a0: kvm_run* run
>> + *  a1: kvm_vcpu* vcpu
>> + */
>> +SYM_FUNC_START(kvm_enter_guest)
>> +    /* allocate space in stack bottom */
>> +    addi.d    a2, sp, -PT_SIZE
>> +    /* save host gprs */
>> +    kvm_save_host_gpr a2
>> +
>> +    /* save host crmd,prmd csr to stack */
>> +    csrrd    a3, LOONGARCH_CSR_CRMD
>> +    st.d    a3, a2, PT_CRMD
>> +    csrrd    a3, LOONGARCH_CSR_PRMD
>> +    st.d    a3, a2, PT_PRMD
>> +
>> +    addi.d    a2, a1, KVM_VCPU_ARCH
>> +    st.d    sp, a2, KVM_ARCH_HSP
>> +    st.d    tp, a2, KVM_ARCH_HTP
>> +    /* Save per cpu register */
>> +    st.d    u0, a2, KVM_ARCH_HPERCPU
>> +
>> +    /* Save kvm_vcpu to kscratch */
>> +    csrwr    a1, KVM_VCPU_KS
>> +    kvm_switch_to_guest
>> +SYM_INNER_LABEL(kvm_enter_guest_end, SYM_L_LOCAL)
>> +SYM_FUNC_END(kvm_enter_guest)
>> +
>> +SYM_FUNC_START(kvm_save_fpu)
>> +    fpu_save_csr    a0 t1
>> +    fpu_save_double a0 t1
>> +    fpu_save_cc    a0 t1 t2
>> +    jr              ra
>> +SYM_FUNC_END(kvm_save_fpu)
>> +
>> +SYM_FUNC_START(kvm_restore_fpu)
>> +    fpu_restore_double a0 t1
>> +    fpu_restore_csr    a0 t1
> This needs to become "fpu_restore_csr a0 t1 t2" after commit 
> bd3c5798484a ("LoongArch: Add Loongson Binary Translation (LBT) 
> extension support") which is slated for Linux 6.6 and already inside 
> linux-next.
I will update it.

Thanks
Tianrui Zhao
>> +    fpu_restore_cc       a0 t1 t2
>> +    jr                 ra
>> +SYM_FUNC_END(kvm_restore_fpu)
>> +
>> +    .section ".rodata"
>> +SYM_DATA(kvm_vector_size, .quad kvm_vector_entry_end - 
>> kvm_vector_entry)
>> +SYM_DATA(kvm_enter_guest_size, .quad kvm_enter_guest_end - 
>> kvm_enter_guest)
>