Re: [PATCH V2 1/2] LoongArch: KVM: Compile the switch.S file directly into the kernel

On 2025/12/22 下午7:34, Xianglai Li wrote:

If we directly compile the switch.S file into the kernel, the address of the kvm_exc_entry function will definitely be within the DMW memory area. Therefore, we will no longer need to perform a copy relocation of kvm_exc_entry.

Based on the above description, compile switch.S directly into the kernel, and then remove the copy relocation execution logic for the kvm_exc_entry function.

Cc: stable@vger.kernel.org Signed-off-by: Xianglai Li lixianglai@loongson.cn

---

Cc: Huacai Chen chenhuacai@kernel.org Cc: WANG Xuerui kernel@xen0n.name Cc: Tianrui Zhao zhaotianrui@loongson.cn Cc: Bibo Mao maobibo@loongson.cn Cc: Charlie Jenkins charlie@rivosinc.com Cc: Xianglai Li lixianglai@loongson.cn Cc: Thomas Gleixner tglx@linutronix.de

arch/loongarch/Kbuild | 2 +- arch/loongarch/include/asm/asm-prototypes.h | 21 +++++++++++++ arch/loongarch/include/asm/kvm_host.h | 3 -- arch/loongarch/kvm/Makefile | 2 +- arch/loongarch/kvm/main.c | 35 ++------------------- arch/loongarch/kvm/switch.S | 22 ++++++++++--- 6 files changed, 43 insertions(+), 42 deletions(-)

diff --git a/arch/loongarch/Kbuild b/arch/loongarch/Kbuild index beb8499dd8ed..1c7a0dbe5e72 100644 --- a/arch/loongarch/Kbuild +++ b/arch/loongarch/Kbuild @@ -3,7 +3,7 @@ obj-y += mm/ obj-y += net/ obj-y += vdso/ -obj-$(CONFIG_KVM) += kvm/ +obj-$(subst m,y,$(CONFIG_KVM)) += kvm/ # for cleaning subdir- += boot diff --git a/arch/loongarch/include/asm/asm-prototypes.h b/arch/loongarch/include/asm/asm-prototypes.h index 704066b4f736..e8ce153691e5 100644 --- a/arch/loongarch/include/asm/asm-prototypes.h +++ b/arch/loongarch/include/asm/asm-prototypes.h @@ -20,3 +20,24 @@ asmlinkage void noinstr __no_stack_protector ret_from_kernel_thread(struct task_ struct pt_regs *regs, int (*fn)(void *), void *fn_arg);

+struct kvm_run; +struct kvm_vcpu;

+void kvm_exc_entry(void); +int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu);

+struct loongarch_fpu;

+#ifdef CONFIG_CPU_HAS_LSX +void kvm_save_lsx(struct loongarch_fpu *fpu); +void kvm_restore_lsx(struct loongarch_fpu *fpu); +#endif

+#ifdef CONFIG_CPU_HAS_LASX +void kvm_save_lasx(struct loongarch_fpu *fpu); +void kvm_restore_lasx(struct loongarch_fpu *fpu); +#endif

+void kvm_save_fpu(struct loongarch_fpu *fpu); +void kvm_restore_fpu(struct loongarch_fpu *fpu); diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h index e4fe5b8e8149..1a1be10e3803 100644 --- a/arch/loongarch/include/asm/kvm_host.h +++ b/arch/loongarch/include/asm/kvm_host.h @@ -85,7 +85,6 @@ struct kvm_context { struct kvm_world_switch { int (*exc_entry)(void); int (*enter_guest)(struct kvm_run *run, struct kvm_vcpu *vcpu);

• unsigned long page_order; };

#define MAX_PGTABLE_LEVELS 4 @@ -347,8 +346,6 @@ void kvm_exc_entry(void); int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu); extern unsigned long vpid_mask; -extern const unsigned long kvm_exception_size; -extern const unsigned long kvm_enter_guest_size; extern struct kvm_world_switch *kvm_loongarch_ops; #define SW_GCSR (1 << 0) diff --git a/arch/loongarch/kvm/Makefile b/arch/loongarch/kvm/Makefile index cb41d9265662..fe665054f824 100644 --- a/arch/loongarch/kvm/Makefile +++ b/arch/loongarch/kvm/Makefile @@ -11,7 +11,7 @@ kvm-y += exit.o kvm-y += interrupt.o kvm-y += main.o kvm-y += mmu.o -kvm-y += switch.o +obj-y += switch.o kvm-y += timer.o kvm-y += tlb.o kvm-y += vcpu.o diff --git a/arch/loongarch/kvm/main.c b/arch/loongarch/kvm/main.c index 80ea63d465b8..67d234540ed4 100644 --- a/arch/loongarch/kvm/main.c +++ b/arch/loongarch/kvm/main.c @@ -340,8 +340,7 @@ void kvm_arch_disable_virtualization_cpu(void) static int kvm_loongarch_env_init(void) {

• int cpu, order, ret;
• void *addr;

• int cpu, ret; struct kvm_context *context;

vmcs = alloc_percpu(struct kvm_context); @@ -357,30 +356,8 @@ static int kvm_loongarch_env_init(void) return -ENOMEM; }

• /*

• * PGD register is shared between root kernel and kvm hypervisor.
  

• * So world switch entry should be in DMW area rather than TLB area
  

• * to avoid page fault reenter.
  

• *
  

• * In future if hardware pagetable walking is supported, we won't
  

• * need to copy world switch code to DMW area.
  

• */
  

• order = get_order(kvm_exception_size + kvm_enter_guest_size);
• addr = (void *)__get_free_pages(GFP_KERNEL, order);
• if (!addr) {

• free_percpu(vmcs);
  

• vmcs = NULL;
  

• kfree(kvm_loongarch_ops);
  

• kvm_loongarch_ops = NULL;
  

• return -ENOMEM;
  

• }
• memcpy(addr, kvm_exc_entry, kvm_exception_size);
• memcpy(addr + kvm_exception_size, kvm_enter_guest, kvm_enter_guest_size);
• flush_icache_range((unsigned long)addr, (unsigned long)addr + kvm_exception_size + kvm_enter_guest_size);
• kvm_loongarch_ops->exc_entry = addr;
• kvm_loongarch_ops->enter_guest = addr + kvm_exception_size;
• kvm_loongarch_ops->page_order = order;

• kvm_loongarch_ops->exc_entry = (void *)kvm_exc_entry;
• kvm_loongarch_ops->enter_guest = (void *)kvm_enter_guest;

vpid_mask = read_csr_gstat(); vpid_mask = (vpid_mask & CSR_GSTAT_GIDBIT) >> CSR_GSTAT_GIDBIT_SHIFT; @@ -414,16 +391,10 @@ static int kvm_loongarch_env_init(void) static void kvm_loongarch_env_exit(void) {

• unsigned long addr;
• if (vmcs) free_percpu(vmcs);

if (kvm_loongarch_ops) {

• if (kvm_loongarch_ops->exc_entry) {
  

• 	addr = (unsigned long)kvm_loongarch_ops->exc_entry;
  

• 	free_pages(addr, kvm_loongarch_ops->page_order);
  

• }
  

  kfree(kvm_loongarch_ops); }

diff --git a/arch/loongarch/kvm/switch.S b/arch/loongarch/kvm/switch.S index f1768b7a6194..93845ce53651 100644 --- a/arch/loongarch/kvm/switch.S +++ b/arch/loongarch/kvm/switch.S @@ -5,6 +5,7 @@ #include <linux/linkage.h> #include <asm/asm.h> +#include <asm/page.h> #include <asm/asmmacro.h> #include <asm/loongarch.h> #include <asm/regdef.h> @@ -100,10 +101,18 @@ * - 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

• *
  

• * PGD register is shared between root kernel and kvm hypervisor.
  

• * So world switch entry should be in DMW area rather than TLB area
  

• * to avoid page fault reenter.
  

• *
  

• * In future if hardware pagetable walking is supported, we won't
  

• * need to copy world switch code to DMW area.
  

  */ .text .cfi_sections .debug_frame SYM_CODE_START(kvm_exc_entry)
• .p2align PAGE_SHIFT UNWIND_HINT_UNDEFINED csrwr a2, KVM_TEMP_KS csrrd a2, KVM_VCPU_KS

@@ -190,8 +199,8 @@ ret_to_host: kvm_restore_host_gpr a2 jr ra -SYM_INNER_LABEL(kvm_exc_entry_end, SYM_L_LOCAL) SYM_CODE_END(kvm_exc_entry) +EXPORT_SYMBOL(kvm_exc_entry) /*

• int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu)

@@ -215,8 +224,8 @@ SYM_FUNC_START(kvm_enter_guest) /* 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) +EXPORT_SYMBOL(kvm_enter_guest) SYM_FUNC_START(kvm_save_fpu) fpu_save_csr a0 t1 @@ -224,6 +233,7 @@ SYM_FUNC_START(kvm_save_fpu) fpu_save_cc a0 t1 t2 jr ra SYM_FUNC_END(kvm_save_fpu) +EXPORT_SYMBOL(kvm_save_fpu)

one small nit, could EXPORT_SYMBOL_FOR_KVM() be used here compared with EXPORT_SYMBOL()?

Regards Bibo Mao

SYM_FUNC_START(kvm_restore_fpu) fpu_restore_double a0 t1 @@ -231,6 +241,7 @@ SYM_FUNC_START(kvm_restore_fpu) fpu_restore_cc a0 t1 t2 jr ra SYM_FUNC_END(kvm_restore_fpu) +EXPORT_SYMBOL(kvm_restore_fpu) #ifdef CONFIG_CPU_HAS_LSX SYM_FUNC_START(kvm_save_lsx) @@ -239,6 +250,7 @@ SYM_FUNC_START(kvm_save_lsx) lsx_save_data a0 t1 jr ra SYM_FUNC_END(kvm_save_lsx) +EXPORT_SYMBOL(kvm_save_lsx) SYM_FUNC_START(kvm_restore_lsx) lsx_restore_data a0 t1 @@ -246,6 +258,7 @@ SYM_FUNC_START(kvm_restore_lsx) fpu_restore_csr a0 t1 t2 jr ra SYM_FUNC_END(kvm_restore_lsx) +EXPORT_SYMBOL(kvm_restore_lsx) #endif #ifdef CONFIG_CPU_HAS_LASX @@ -255,6 +268,7 @@ SYM_FUNC_START(kvm_save_lasx) lasx_save_data a0 t1 jr ra SYM_FUNC_END(kvm_save_lasx) +EXPORT_SYMBOL(kvm_save_lasx) SYM_FUNC_START(kvm_restore_lasx) lasx_restore_data a0 t1 @@ -262,10 +276,8 @@ SYM_FUNC_START(kvm_restore_lasx) fpu_restore_csr a0 t1 t2 jr ra SYM_FUNC_END(kvm_restore_lasx) +EXPORT_SYMBOL(kvm_restore_lasx) #endif

• .section ".rodata"

-SYM_DATA(kvm_exception_size, .quad kvm_exc_entry_end - kvm_exc_entry) -SYM_DATA(kvm_enter_guest_size, .quad kvm_enter_guest_end - kvm_enter_guest) #ifdef CONFIG_CPU_HAS_LBT STACK_FRAME_NON_STANDARD kvm_restore_fpu