Re: [PATCH V2 1/2] LoongArch: KVM: Compile the switch.S file directly into the kernel
From: lixianglai
Date: Mon Dec 22 2025 - 21:38:46 EST
Hi Bibo Mao:
On 2025/12/22 下午7:34, Xianglai Li wrote:
If we directly compile the switch.S file into the kernel, the address ofone small nit, could EXPORT_SYMBOL_FOR_KVM() be used here compared with EXPORT_SYMBOL()?
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@xxxxxxxxxxxxxxx
Signed-off-by: Xianglai Li <lixianglai@xxxxxxxxxxx>
---
Cc: Huacai Chen <chenhuacai@xxxxxxxxxx>
Cc: WANG Xuerui <kernel@xxxxxxxxxx>
Cc: Tianrui Zhao <zhaotianrui@xxxxxxxxxxx>
Cc: Bibo Mao <maobibo@xxxxxxxxxxx>
Cc: Charlie Jenkins <charlie@xxxxxxxxxxxx>
Cc: Xianglai Li <lixianglai@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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)
Ok! will fix it in next version
Thanks!
Xianglai.
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