KVM: PPC: Book3S HV P9: Use Linux SPR save/restore to manage some host SPRs

Linux implements SPR save/restore including storage space for registers
in the task struct for process context switching. Make use of this
similarly to the way we make use of the context switching fp/vec save
restore.

This improves code reuse, allows some stack space to be saved, and helps
with avoiding VRSAVE updates if they are not required.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211123095231.1036501-39-npiggin@gmail.com

diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h
index e8013cd..1f43ef6 100644 (file)
--- a/arch/powerpc/include/asm/switch_to.h
+++ b/arch/powerpc/include/asm/switch_to.h
@@ -113,6 +113,7 @@ static inline void clear_task_ebb(struct task_struct *t)
 }
 
 void kvmppc_save_user_regs(void);
+void kvmppc_save_current_sprs(void);
 
 extern int set_thread_tidr(struct task_struct *t);
 

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 8f841fb..5d2333d 100644 (file)
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1182,6 +1182,12 @@ void kvmppc_save_user_regs(void)
 #endif
 }
 EXPORT_SYMBOL_GPL(kvmppc_save_user_regs);
+
+void kvmppc_save_current_sprs(void)
+{
+       save_sprs(&current->thread);
+}
+EXPORT_SYMBOL_GPL(kvmppc_save_current_sprs);
 #endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */
 
 static inline void restore_sprs(struct thread_struct *old_thread,

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 198f6d9..7d48aa8 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4566,9 +4566,6 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
        struct kvm_run *run = vcpu->run;
        int r;
        int srcu_idx;
-       unsigned long ebb_regs[3] = {}; /* shut up GCC */
-       unsigned long user_tar = 0;
-       unsigned int user_vrsave;
        struct kvm *kvm;
        unsigned long msr;
 
@@ -4629,14 +4626,7 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
 
        kvmppc_save_user_regs();
 
-       /* Save userspace EBB and other register values */
-       if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
-               ebb_regs[0] = mfspr(SPRN_EBBHR);
-               ebb_regs[1] = mfspr(SPRN_EBBRR);
-               ebb_regs[2] = mfspr(SPRN_BESCR);
-               user_tar = mfspr(SPRN_TAR);
-       }
-       user_vrsave = mfspr(SPRN_VRSAVE);
+       kvmppc_save_current_sprs();
 
        vcpu->arch.waitp = &vcpu->arch.vcore->wait;
        vcpu->arch.pgdir = kvm->mm->pgd;
@@ -4677,15 +4667,6 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
                }
        } while (is_kvmppc_resume_guest(r));
 
-       /* Restore userspace EBB and other register values */
-       if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
-               mtspr(SPRN_EBBHR, ebb_regs[0]);
-               mtspr(SPRN_EBBRR, ebb_regs[1]);
-               mtspr(SPRN_BESCR, ebb_regs[2]);
-               mtspr(SPRN_TAR, user_tar);
-       }
-       mtspr(SPRN_VRSAVE, user_vrsave);
-
        vcpu->arch.state = KVMPPC_VCPU_NOTREADY;
        atomic_dec(&kvm->arch.vcpus_running);
 

diff --git a/arch/powerpc/kvm/book3s_hv.h b/arch/powerpc/kvm/book3s_hv.h
index d7485b9..6b7f07d 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv.h
+++ b/arch/powerpc/kvm/book3s_hv.h
@@ -4,11 +4,8 @@
  * Privileged (non-hypervisor) host registers to save.
  */
 struct p9_host_os_sprs {
-       unsigned long dscr;
-       unsigned long tidr;
        unsigned long iamr;
        unsigned long amr;
-       unsigned long fscr;
 
        unsigned int pmc1;
        unsigned int pmc2;

diff --git a/arch/powerpc/kvm/book3s_hv_p9_entry.c b/arch/powerpc/kvm/book3s_hv_p9_entry.c
index 8499e8a..093ac04 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv_p9_entry.c
+++ b/arch/powerpc/kvm/book3s_hv_p9_entry.c
@@ -231,15 +231,26 @@ EXPORT_SYMBOL_GPL(switch_pmu_to_host);
 static void load_spr_state(struct kvm_vcpu *vcpu,
                                struct p9_host_os_sprs *host_os_sprs)
 {
+       /* TAR is very fast */
        mtspr(SPRN_TAR, vcpu->arch.tar);
 
+#ifdef CONFIG_ALTIVEC
+       if (cpu_has_feature(CPU_FTR_ALTIVEC) &&
+           current->thread.vrsave != vcpu->arch.vrsave)
+               mtspr(SPRN_VRSAVE, vcpu->arch.vrsave);
+#endif
+
        if (vcpu->arch.hfscr & HFSCR_EBB) {
-               mtspr(SPRN_EBBHR, vcpu->arch.ebbhr);
-               mtspr(SPRN_EBBRR, vcpu->arch.ebbrr);
-               mtspr(SPRN_BESCR, vcpu->arch.bescr);
+               if (current->thread.ebbhr != vcpu->arch.ebbhr)
+                       mtspr(SPRN_EBBHR, vcpu->arch.ebbhr);
+               if (current->thread.ebbrr != vcpu->arch.ebbrr)
+                       mtspr(SPRN_EBBRR, vcpu->arch.ebbrr);
+               if (current->thread.bescr != vcpu->arch.bescr)
+                       mtspr(SPRN_BESCR, vcpu->arch.bescr);
        }
 
-       if (cpu_has_feature(CPU_FTR_P9_TIDR))
+       if (cpu_has_feature(CPU_FTR_P9_TIDR) &&
+                       current->thread.tidr != vcpu->arch.tid)
                mtspr(SPRN_TIDR, vcpu->arch.tid);
        if (host_os_sprs->iamr != vcpu->arch.iamr)
                mtspr(SPRN_IAMR, vcpu->arch.iamr);
@@ -247,9 +258,9 @@ static void load_spr_state(struct kvm_vcpu *vcpu,
                mtspr(SPRN_AMR, vcpu->arch.amr);
        if (vcpu->arch.uamor != 0)
                mtspr(SPRN_UAMOR, vcpu->arch.uamor);
-       if (host_os_sprs->fscr != vcpu->arch.fscr)
+       if (current->thread.fscr != vcpu->arch.fscr)
                mtspr(SPRN_FSCR, vcpu->arch.fscr);
-       if (host_os_sprs->dscr != vcpu->arch.dscr)
+       if (current->thread.dscr != vcpu->arch.dscr)
                mtspr(SPRN_DSCR, vcpu->arch.dscr);
        if (vcpu->arch.pspb != 0)
                mtspr(SPRN_PSPB, vcpu->arch.pspb);
@@ -269,20 +280,15 @@ static void store_spr_state(struct kvm_vcpu *vcpu)
 {
        vcpu->arch.tar = mfspr(SPRN_TAR);
 
+#ifdef CONFIG_ALTIVEC
+       if (cpu_has_feature(CPU_FTR_ALTIVEC))
+               vcpu->arch.vrsave = mfspr(SPRN_VRSAVE);
+#endif
+
        if (vcpu->arch.hfscr & HFSCR_EBB) {
                vcpu->arch.ebbhr = mfspr(SPRN_EBBHR);
                vcpu->arch.ebbrr = mfspr(SPRN_EBBRR);
                vcpu->arch.bescr = mfspr(SPRN_BESCR);
-               /*
-                * This is like load_fp in context switching, turn off the
-                * facility after it wraps the u8 to try avoiding saving
-                * and restoring the registers each partition switch.
-                */
-               if (!vcpu->arch.nested) {
-                       vcpu->arch.load_ebb++;
-                       if (!vcpu->arch.load_ebb)
-                               vcpu->arch.hfscr &= ~HFSCR_EBB;
-               }
        }
 
        if (cpu_has_feature(CPU_FTR_P9_TIDR))
@@ -324,7 +330,6 @@ bool load_vcpu_state(struct kvm_vcpu *vcpu,
 #ifdef CONFIG_ALTIVEC
        load_vr_state(&vcpu->arch.vr);
 #endif
-       mtspr(SPRN_VRSAVE, vcpu->arch.vrsave);
 
        return ret;
 }
@@ -338,7 +343,6 @@ void store_vcpu_state(struct kvm_vcpu *vcpu)
 #ifdef CONFIG_ALTIVEC
        store_vr_state(&vcpu->arch.vr);
 #endif
-       vcpu->arch.vrsave = mfspr(SPRN_VRSAVE);
 
 #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
        if (cpu_has_feature(CPU_FTR_TM) ||
@@ -364,12 +368,8 @@ EXPORT_SYMBOL_GPL(store_vcpu_state);
 
 void save_p9_host_os_sprs(struct p9_host_os_sprs *host_os_sprs)
 {
-       if (cpu_has_feature(CPU_FTR_P9_TIDR))
-               host_os_sprs->tidr = mfspr(SPRN_TIDR);
        host_os_sprs->iamr = mfspr(SPRN_IAMR);
        host_os_sprs->amr = mfspr(SPRN_AMR);
-       host_os_sprs->fscr = mfspr(SPRN_FSCR);
-       host_os_sprs->dscr = mfspr(SPRN_DSCR);
 }
 EXPORT_SYMBOL_GPL(save_p9_host_os_sprs);
 
@@ -377,26 +377,63 @@ EXPORT_SYMBOL_GPL(save_p9_host_os_sprs);
 void restore_p9_host_os_sprs(struct kvm_vcpu *vcpu,
                             struct p9_host_os_sprs *host_os_sprs)
 {
+       /*
+        * current->thread.xxx registers must all be restored to host
+        * values before a potential context switch, othrewise the context
+        * switch itself will overwrite current->thread.xxx with the values
+        * from the guest SPRs.
+        */
+
        mtspr(SPRN_SPRG_VDSO_WRITE, local_paca->sprg_vdso);
 
-       if (cpu_has_feature(CPU_FTR_P9_TIDR))
-               mtspr(SPRN_TIDR, host_os_sprs->tidr);
+       if (cpu_has_feature(CPU_FTR_P9_TIDR) &&
+                       current->thread.tidr != vcpu->arch.tid)
+               mtspr(SPRN_TIDR, current->thread.tidr);
        if (host_os_sprs->iamr != vcpu->arch.iamr)
                mtspr(SPRN_IAMR, host_os_sprs->iamr);
        if (vcpu->arch.uamor != 0)
                mtspr(SPRN_UAMOR, 0);
        if (host_os_sprs->amr != vcpu->arch.amr)
                mtspr(SPRN_AMR, host_os_sprs->amr);
-       if (host_os_sprs->fscr != vcpu->arch.fscr)
-               mtspr(SPRN_FSCR, host_os_sprs->fscr);
-       if (host_os_sprs->dscr != vcpu->arch.dscr)
-               mtspr(SPRN_DSCR, host_os_sprs->dscr);
+       if (current->thread.fscr != vcpu->arch.fscr)
+               mtspr(SPRN_FSCR, current->thread.fscr);
+       if (current->thread.dscr != vcpu->arch.dscr)
+               mtspr(SPRN_DSCR, current->thread.dscr);
        if (vcpu->arch.pspb != 0)
                mtspr(SPRN_PSPB, 0);
 
        /* Save guest CTRL register, set runlatch to 1 */
        if (!(vcpu->arch.ctrl & 1))
                mtspr(SPRN_CTRLT, 1);
+
+#ifdef CONFIG_ALTIVEC
+       if (cpu_has_feature(CPU_FTR_ALTIVEC) &&
+           vcpu->arch.vrsave != current->thread.vrsave)
+               mtspr(SPRN_VRSAVE, current->thread.vrsave);
+#endif
+       if (vcpu->arch.hfscr & HFSCR_EBB) {
+               if (vcpu->arch.bescr != current->thread.bescr)
+                       mtspr(SPRN_BESCR, current->thread.bescr);
+               if (vcpu->arch.ebbhr != current->thread.ebbhr)
+                       mtspr(SPRN_EBBHR, current->thread.ebbhr);
+               if (vcpu->arch.ebbrr != current->thread.ebbrr)
+                       mtspr(SPRN_EBBRR, current->thread.ebbrr);
+
+               if (!vcpu->arch.nested) {
+                       /*
+                        * This is like load_fp in context switching, turn off
+                        * the facility after it wraps the u8 to try avoiding
+                        * saving and restoring the registers each partition
+                        * switch.
+                        */
+                       vcpu->arch.load_ebb++;
+                       if (!vcpu->arch.load_ebb)
+                               vcpu->arch.hfscr &= ~HFSCR_EBB;
+               }
+       }
+
+       if (vcpu->arch.tar != current->thread.tar)
+               mtspr(SPRN_TAR, current->thread.tar);
 }
 EXPORT_SYMBOL_GPL(restore_p9_host_os_sprs);