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[PATCH] target/s390x/kvm: Simplify the async pfault handling code

Thomas Huth posted 1 patch 2 weeks, 6 days ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20260317134531.460141-1-thuth@redhat.com
Maintainers: Halil Pasic <pasic@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, Eric Farman <farman@linux.ibm.com>, Matthew Rosato <mjrosato@linux.ibm.com>, Cornelia Huck <cohuck@redhat.com>, Richard Henderson <richard.henderson@linaro.org>, Ilya Leoshkevich <iii@linux.ibm.com>, David Hildenbrand <david@kernel.org>
target/s390x/kvm/kvm.c | 52 +++++++++---------------------------------
1 file changed, 11 insertions(+), 41 deletions(-)
[PATCH] target/s390x/kvm: Simplify the async pfault handling code
Posted by Thomas Huth 2 weeks, 6 days ago 
From: Thomas Huth <thuth@redhat.com>

Since commit 126e7f78036 ("kvm: require KVM_CAP_IOEVENTFD and
KVM_CAP_IOEVENTFD_ANY_LENGTH") we require at least kernel v4.4 to
be able to use KVM. KVM_CAP_ASYNC_PF is available in the kernel
since v3.15 and KVM_SYNC_PFAULT is available since kernel v3.18,
so we can assume now that they are available in all supported
kernels. Thus simplify the code a little bit by removing the
checks for these features.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 I just found this old patch on one of my local branches ... seems like
 I forgot to send it out after writing it last year...

 target/s390x/kvm/kvm.c | 52 +++++++++---------------------------------
 1 file changed, 11 insertions(+), 41 deletions(-)

diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
index 54d28e37d4d..133e8c12fd4 100644
--- a/target/s390x/kvm/kvm.c
+++ b/target/s390x/kvm/kvm.c
@@ -140,7 +140,6 @@ const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
     KVM_CAP_LAST_INFO
 };
 
-static int cap_async_pf;
 static int cap_mem_op;
 static int cap_mem_op_extension;
 static int cap_s390_irq;
@@ -333,6 +332,7 @@ int kvm_arch_get_default_type(MachineState *ms)
 int kvm_arch_init(MachineState *ms, KVMState *s)
 {
     int required_caps[] = {
+        KVM_CAP_ASYNC_PF,
         KVM_CAP_DEVICE_CTRL,
         KVM_CAP_SYNC_REGS,
     };
@@ -340,7 +340,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
     for (int i = 0; i < ARRAY_SIZE(required_caps); i++) {
         if (!kvm_check_extension(s, required_caps[i])) {
             error_report("KVM is missing capability #%d - "
-                         "please use kernel 3.15 or newer", required_caps[i]);
+                         "please use kernel 4.4 or newer", required_caps[i]);
             return -1;
         }
     }
@@ -354,7 +354,6 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
         return -1;
     }
 
-    cap_async_pf = kvm_check_extension(s, KVM_CAP_ASYNC_PF);
     cap_mem_op = kvm_check_extension(s, KVM_CAP_S390_MEM_OP);
     cap_mem_op_extension = kvm_check_extension(s, KVM_CAP_S390_MEM_OP_EXTENSION);
     mem_op_storage_key_support = cap_mem_op_extension > 0;
@@ -466,7 +465,8 @@ static int can_sync_regs(CPUState *cs, int regs)
 }
 
 #define KVM_SYNC_REQUIRED_REGS (KVM_SYNC_GPRS | KVM_SYNC_ACRS | \
-                                KVM_SYNC_CRS | KVM_SYNC_PREFIX)
+                                KVM_SYNC_CRS | KVM_SYNC_PREFIX | \
+                                KVM_SYNC_PFAULT)
 
 int kvm_arch_put_registers(CPUState *cs, KvmPutState level, Error **errp)
 {
@@ -550,25 +550,10 @@ int kvm_arch_put_registers(CPUState *cs, KvmPutState level, Error **errp)
     }
 
     /* pfault parameters */
-    if (can_sync_regs(cs, KVM_SYNC_PFAULT)) {
-        cs->kvm_run->s.regs.pft = env->pfault_token;
-        cs->kvm_run->s.regs.pfs = env->pfault_select;
-        cs->kvm_run->s.regs.pfc = env->pfault_compare;
-        cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_PFAULT;
-    } else if (cap_async_pf) {
-        r = kvm_set_one_reg(cs, KVM_REG_S390_PFTOKEN, &env->pfault_token);
-        if (r < 0) {
-            return r;
-        }
-        r = kvm_set_one_reg(cs, KVM_REG_S390_PFCOMPARE, &env->pfault_compare);
-        if (r < 0) {
-            return r;
-        }
-        r = kvm_set_one_reg(cs, KVM_REG_S390_PFSELECT, &env->pfault_select);
-        if (r < 0) {
-            return r;
-        }
-    }
+    cs->kvm_run->s.regs.pft = env->pfault_token;
+    cs->kvm_run->s.regs.pfs = env->pfault_select;
+    cs->kvm_run->s.regs.pfc = env->pfault_compare;
+    cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_PFAULT;
 
     if (can_sync_regs(cs, KVM_SYNC_GSCB)) {
         memcpy(cs->kvm_run->s.regs.gscb, env->gscb, 32);
@@ -673,24 +658,9 @@ int kvm_arch_get_registers(CPUState *cs, Error **errp)
     }
 
     /* pfault parameters */
-    if (can_sync_regs(cs, KVM_SYNC_PFAULT)) {
-        env->pfault_token = cs->kvm_run->s.regs.pft;
-        env->pfault_select = cs->kvm_run->s.regs.pfs;
-        env->pfault_compare = cs->kvm_run->s.regs.pfc;
-    } else if (cap_async_pf) {
-        r = kvm_get_one_reg(cs, KVM_REG_S390_PFTOKEN, &env->pfault_token);
-        if (r < 0) {
-            return r;
-        }
-        r = kvm_get_one_reg(cs, KVM_REG_S390_PFCOMPARE, &env->pfault_compare);
-        if (r < 0) {
-            return r;
-        }
-        r = kvm_get_one_reg(cs, KVM_REG_S390_PFSELECT, &env->pfault_select);
-        if (r < 0) {
-            return r;
-        }
-    }
+    env->pfault_token = cs->kvm_run->s.regs.pft;
+    env->pfault_select = cs->kvm_run->s.regs.pfs;
+    env->pfault_compare = cs->kvm_run->s.regs.pfc;
 
     if (can_sync_regs(cs, KVM_SYNC_DIAG318)) {
         env->diag318_info = cs->kvm_run->s.regs.diag318;
-- 
2.53.0
Re: [PATCH] target/s390x/kvm: Simplify the async pfault handling code
Posted by Eric Farman 2 weeks ago 
On Tue, 2026-03-17 at 14:45 +0100, Thomas Huth wrote:
> From: Thomas Huth <thuth@redhat.com>
> 
> Since commit 126e7f78036 ("kvm: require KVM_CAP_IOEVENTFD and
> KVM_CAP_IOEVENTFD_ANY_LENGTH") we require at least kernel v4.4 to
> be able to use KVM. KVM_CAP_ASYNC_PF is available in the kernel
> since v3.15 and KVM_SYNC_PFAULT is available since kernel v3.18,
> so we can assume now that they are available in all supported
> kernels. Thus simplify the code a little bit by removing the
> checks for these features.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  I just found this old patch on one of my local branches ... seems like
>  I forgot to send it out after writing it last year...
> 
>  target/s390x/kvm/kvm.c | 52 +++++++++---------------------------------
>  1 file changed, 11 insertions(+), 41 deletions(-)

Nice.

Reviewed-by: Eric Farman <farman@linux.ibm.com>
Re: [PATCH] target/s390x/kvm: Simplify the async pfault handling code
Posted by Matthew Rosato 2 weeks, 6 days ago 
On 3/17/26 9:45 AM, Thomas Huth wrote:
> From: Thomas Huth <thuth@redhat.com>
> 
> Since commit 126e7f78036 ("kvm: require KVM_CAP_IOEVENTFD and
> KVM_CAP_IOEVENTFD_ANY_LENGTH") we require at least kernel v4.4 to
> be able to use KVM. KVM_CAP_ASYNC_PF is available in the kernel
> since v3.15 and KVM_SYNC_PFAULT is available since kernel v3.18,
> so we can assume now that they are available in all supported
> kernels. Thus simplify the code a little bit by removing the
> checks for these features.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>

LGTM, thanks Thomas!

Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Re: [PATCH] target/s390x/kvm: Simplify the async pfault handling code
Posted by Christian Borntraeger 2 weeks, 6 days ago 
Am 17.03.26 um 14:45 schrieb Thomas Huth:
> From: Thomas Huth <thuth@redhat.com>
> 
> Since commit 126e7f78036 ("kvm: require KVM_CAP_IOEVENTFD and
> KVM_CAP_IOEVENTFD_ANY_LENGTH") we require at least kernel v4.4 to
> be able to use KVM. KVM_CAP_ASYNC_PF is available in the kernel
> since v3.15 and KVM_SYNC_PFAULT is available since kernel v3.18,
> so we can assume now that they are available in all supported
> kernels. Thus simplify the code a little bit by removing the
> checks for these features.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>

Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>

Patchew 2.1-devel-ea86937

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