Re: [PATCH V4 1/2] LoongArch: KVM: Compile the switch.S file directly into the kernel
From: lixianglai
Date: Mon Apr 27 2026 - 04:48:37 EST
Hi Huacai Chen:
Hi, Xianglai,Oh~ Here, we should use SYM_FUNC_START/SYM_FUNC_END. I also reproduced this issue locally.
After this patch I get:
arch/loongarch/kvm/switch.o: warning: objtool: kvm_enter_guest+0x0:
unreachable instruction
But if I restore SYM_FUNC_START/SYM_FUNC_END for kvm_enter_guest, the
warning disappear. So please make sure which one is correct.
After making the modification, the compilation did not notice this compilation warning.
Thanks,
Xianglai.
Huacai
On Tue, Apr 14, 2026 at 7:57 PM Xianglai Li <lixianglai@xxxxxxxxxxx> 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.
Signed-off-by: Xianglai Li <lixianglai@xxxxxxxxxxx>
---
Cc: Huacai Chen <chenhuacai@xxxxxxxxxx>
Cc: Tianrui Zhao <zhaotianrui@xxxxxxxxxxx>
Cc: Bibo Mao <maobibo@xxxxxxxxxxx>
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 | 27 +++++++++++-----
6 files changed, 46 insertions(+), 44 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 19eb5e5c3984..0bcdffc14c5f 100644
--- a/arch/loongarch/include/asm/kvm_host.h
+++ b/arch/loongarch/include/asm/kvm_host.h
@@ -86,7 +86,6 @@ 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
@@ -356,8 +355,6 @@ 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 2c593ac7892f..18800a38b150 100644
--- a/arch/loongarch/kvm/main.c
+++ b/arch/loongarch/kvm/main.c
@@ -348,8 +348,7 @@ 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);
@@ -365,30 +364,8 @@ 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;
@@ -422,16 +399,10 @@ 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..1a5636790ef9 100644
--- a/arch/loongarch/kvm/switch.S
+++ b/arch/loongarch/kvm/switch.S
@@ -5,10 +5,12 @@
#include <linux/linkage.h>
#include <asm/asm.h>
+#include <asm/page.h>
#include <asm/asmmacro.h>
#include <asm/loongarch.h>
#include <asm/regdef.h>
#include <asm/unwind_hints.h>
+#include <linux/kvm_types.h>
#define HGPR_OFFSET(x) (PT_R0 + 8*x)
#define GGPR_OFFSET(x) (KVM_ARCH_GGPR + 8*x)
@@ -100,8 +102,16 @@
* - 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
+ .p2align PAGE_SHIFT
.cfi_sections .debug_frame
SYM_CODE_START(kvm_exc_entry)
UNWIND_HINT_UNDEFINED
@@ -190,8 +200,8 @@ 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_FOR_KVM(kvm_exc_entry)
/*
* int kvm_enter_guest(struct kvm_run *run, struct kvm_vcpu *vcpu)
@@ -200,7 +210,7 @@ SYM_CODE_END(kvm_exc_entry)
* a0: kvm_run* run
* a1: kvm_vcpu* vcpu
*/
-SYM_FUNC_START(kvm_enter_guest)
+SYM_CODE_START(kvm_enter_guest)
/* Allocate space in stack bottom */
addi.d a2, sp, -PT_SIZE
/* Save host GPRs */
@@ -215,8 +225,8 @@ 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)
+SYM_CODE_END(kvm_enter_guest)
+EXPORT_SYMBOL_FOR_KVM(kvm_enter_guest)
SYM_FUNC_START(kvm_save_fpu)
fpu_save_csr a0 t1
@@ -224,6 +234,7 @@ SYM_FUNC_START(kvm_save_fpu)
fpu_save_cc a0 t1 t2
jr ra
SYM_FUNC_END(kvm_save_fpu)
+EXPORT_SYMBOL_FOR_KVM(kvm_save_fpu)
SYM_FUNC_START(kvm_restore_fpu)
fpu_restore_double a0 t1
@@ -231,6 +242,7 @@ SYM_FUNC_START(kvm_restore_fpu)
fpu_restore_cc a0 t1 t2
jr ra
SYM_FUNC_END(kvm_restore_fpu)
+EXPORT_SYMBOL_FOR_KVM(kvm_restore_fpu)
#ifdef CONFIG_CPU_HAS_LSX
SYM_FUNC_START(kvm_save_lsx)
@@ -239,6 +251,7 @@ SYM_FUNC_START(kvm_save_lsx)
lsx_save_data a0 t1
jr ra
SYM_FUNC_END(kvm_save_lsx)
+EXPORT_SYMBOL_FOR_KVM(kvm_save_lsx)
SYM_FUNC_START(kvm_restore_lsx)
lsx_restore_data a0 t1
@@ -246,6 +259,7 @@ SYM_FUNC_START(kvm_restore_lsx)
fpu_restore_csr a0 t1 t2
jr ra
SYM_FUNC_END(kvm_restore_lsx)
+EXPORT_SYMBOL_FOR_KVM(kvm_restore_lsx)
#endif
#ifdef CONFIG_CPU_HAS_LASX
@@ -255,6 +269,7 @@ SYM_FUNC_START(kvm_save_lasx)
lasx_save_data a0 t1
jr ra
SYM_FUNC_END(kvm_save_lasx)
+EXPORT_SYMBOL_FOR_KVM(kvm_save_lasx)
SYM_FUNC_START(kvm_restore_lasx)
lasx_restore_data a0 t1
@@ -262,10 +277,8 @@ SYM_FUNC_START(kvm_restore_lasx)
fpu_restore_csr a0 t1 t2
jr ra
SYM_FUNC_END(kvm_restore_lasx)
+EXPORT_SYMBOL_FOR_KVM(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
--
2.39.1