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Tue, 25 Nov 2025 07:46:08 +0000 (GMT) From: Andrew Donnellan Date: Tue, 25 Nov 2025 18:45:52 +1100 Subject: [PATCH 1/3] KVM: s390: Add signal_exits counter Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20251125-s390-kvm-xfer-to-guest-work-v1-1-091281a34611@linux.ibm.com> References: <20251125-s390-kvm-xfer-to-guest-work-v1-0-091281a34611@linux.ibm.com> In-Reply-To: <20251125-s390-kvm-xfer-to-guest-work-v1-0-091281a34611@linux.ibm.com> To: kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Sven Schnelle Cc: Nicholas Miehlbradt , Thomas Gleixner , Peter Zijlstra , Andy Lutomirski , David Hildenbrand X-Mailer: b4 0.14.2 X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTIyMDAyMSBTYWx0ZWRfX93/PiJrgs8IA AaudWQWICpxTav2KBwI7EYLtFJ7/PN0ReI60Ni+P2OKGorQvcNAfnVWhRBPLQ2PSQRUSBGyib0l Zx2hFxBB1iF6bf7mD+V5ibsNsySsRhzoG2lYWdyujOuINzXP9ImgkynhpVRDkdhREbHJ6ym2asg GZq0MH9OG9evRTQiC5rrmpAPSM+vIqqJXiSH2GRL2fASIJzxLjB5l009JmFAYQA1cEjR6iflOgZ ChVveIa4MpAnfLmm0Rwh/sfOdiUeEKFYPy6DFNwir+I4zXpH313GBLb9pAZ8keAN3W0MqPAesTd uAUlF/pQ/4/u/x3alNfqcH/oV3p1eW/Jv0X16yDaO85QplHs+T+DA+3h41zsgXkpY81gQuEzmWx IMHXIXV4z8kWqjyCc7iUsOKKxIgPGQ== X-Proofpoint-ORIG-GUID: wF2B8_1XnB89yi7T06xI9BN2aSoZbrKe X-Proofpoint-GUID: wF2B8_1XnB89yi7T06xI9BN2aSoZbrKe X-Authority-Analysis: v=2.4 cv=TMJIilla c=1 sm=1 tr=0 ts=69255eca cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=G-lmFN37WTdQfOt6kDkA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-25_02,2025-11-24_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 spamscore=0 phishscore=0 impostorscore=0 clxscore=1015 adultscore=0 bulkscore=0 suspectscore=0 malwarescore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511220021 Add a signal_exits counter for s390, as exists on arm64, loongarch, mips, powerpc, riscv and x86. This is used by kvm_handle_signal_exit(), which we will use when we later enable CONFIG_VIRT_XFER_TO_GUEST_WORK. Signed-off-by: Andrew Donnellan --- arch/s390/include/asm/kvm_host.h | 1 + arch/s390/kvm/kvm-s390.c | 4 +++- 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_h= ost.h index c2ba3d4398c5371526ddfd53b43607c00abc35a1..1b08a250fb341f7bd2d19810392= c1c6e21673b64 100644 --- a/arch/s390/include/asm/kvm_host.h +++ b/arch/s390/include/asm/kvm_host.h @@ -146,6 +146,7 @@ struct kvm_vcpu_stat { u64 instruction_diagnose_500; u64 instruction_diagnose_other; u64 pfault_sync; + u64 signal_exits; }; =20 #define PGM_OPERATION 0x01 diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 16ba04062854a99ab7d48ac427b690006ea8e7eb..fa6b5150ca31e4d9f0bdafabc1f= b1d90ef3f3d0d 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -185,7 +185,8 @@ const struct _kvm_stats_desc kvm_vcpu_stats_desc[] =3D { STATS_DESC_COUNTER(VCPU, instruction_diagnose_308), STATS_DESC_COUNTER(VCPU, instruction_diagnose_500), STATS_DESC_COUNTER(VCPU, instruction_diagnose_other), - STATS_DESC_COUNTER(VCPU, pfault_sync) + STATS_DESC_COUNTER(VCPU, pfault_sync), + STATS_DESC_COUNTER(VCPU, signal_exits) }; 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Enabling interrupts only after the __TI_sie flag has been set guarantees that the SIE instruction is not executed if an interrupt happens between enabling interrupts and the execution of the SIE instruction. Interrupt handlers and machine check handler forward the PSW to the sie_exit label in such cases. This is a prerequisite for VIRT_XFER_TO_GUEST_WORK to prevent that guest context is entered when e.g. a scheduler IPI, indicating that a reschedule is required, happens right before the SIE instruction, which could lead to long delays. Signed-off-by: Heiko Carstens Tested-by: Andrew Donnellan Signed-off-by: Andrew Donnellan --- arch/s390/include/asm/stacktrace.h | 1 + arch/s390/kernel/asm-offsets.c | 1 + arch/s390/kernel/entry.S | 2 ++ arch/s390/kvm/kvm-s390.c | 5 ----- 4 files changed, 4 insertions(+), 5 deletions(-) diff --git a/arch/s390/include/asm/stacktrace.h b/arch/s390/include/asm/sta= cktrace.h index 810a6b9d96280f73311de873ad180c59a0cfbd5f..c9ae680a28af910c4703eee179b= e4db6c1ec9ad1 100644 --- a/arch/s390/include/asm/stacktrace.h +++ b/arch/s390/include/asm/stacktrace.h @@ -66,6 +66,7 @@ struct stack_frame { unsigned long sie_flags; unsigned long sie_control_block_phys; unsigned long sie_guest_asce; + unsigned long sie_irq; }; }; unsigned long gprs[10]; diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c index a8915663e917faed4551276b64013ee073662cc9..730449f464aff25761264b00d63= d92e907f17f78 100644 --- a/arch/s390/kernel/asm-offsets.c +++ b/arch/s390/kernel/asm-offsets.c @@ -64,6 +64,7 @@ int main(void) OFFSET(__SF_SIE_FLAGS, stack_frame, sie_flags); OFFSET(__SF_SIE_CONTROL_PHYS, stack_frame, sie_control_block_phys); OFFSET(__SF_SIE_GUEST_ASCE, stack_frame, sie_guest_asce); + OFFSET(__SF_SIE_IRQ, stack_frame, sie_irq); DEFINE(STACK_FRAME_OVERHEAD, sizeof(struct stack_frame)); BLANK(); OFFSET(__SFUSER_BACKCHAIN, stack_frame_user, back_chain); diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S index 75b0fbb236d05f420b20cac6bac925e8ac36fa68..e906f4ab6cf35e53061a2719291= 1629c10c347ed 100644 --- a/arch/s390/kernel/entry.S +++ b/arch/s390/kernel/entry.S @@ -189,6 +189,7 @@ SYM_FUNC_START(__sie64a) mvc __SF_SIE_FLAGS(8,%r15),__TI_flags(%r14) # copy thread flags lmg %r0,%r13,0(%r4) # load guest gprs 0-13 mvi __TI_sie(%r14),1 + stosm __SF_SIE_IRQ(%r15),0x03 # enable interrupts lctlg %c1,%c1,__SF_SIE_GUEST_ASCE(%r15) # load primary asce lg %r14,__SF_SIE_CONTROL(%r15) # get control block pointer oi __SIE_PROG0C+3(%r14),1 # we are going into SIE now @@ -212,6 +213,7 @@ SYM_FUNC_START(__sie64a) lg %r14,__LC_CURRENT(%r14) mvi __TI_sie(%r14),0 SYM_INNER_LABEL(sie_exit, SYM_L_GLOBAL) + stnsm __SF_SIE_IRQ(%r15),0xfc # disable interrupts lg %r14,__SF_SIE_SAVEAREA(%r15) # load guest register save area stmg %r0,%r13,0(%r14) # save guest gprs 0-13 xgr %r0,%r0 # clear guest registers to diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index fa6b5150ca31e4d9f0bdafabc1fb1d90ef3f3d0d..3cad08662b3d80aaf6f5f8891fc= 08b383c3c44d4 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -5075,13 +5075,8 @@ int noinstr kvm_s390_enter_exit_sie(struct kvm_s390_= sie_block *scb, * The guest_state_{enter,exit}_irqoff() functions inform lockdep and * tracing that entry to the guest will enable host IRQs, and exit from * the guest will disable host IRQs. - * - * We must not use lockdep/tracing/RCU in this critical section, so we - * use the low-level arch_local_irq_*() helpers to enable/disable IRQs. */ - arch_local_irq_enable(); 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The exittime tests from kvm-unit-tests, in my tests, were +/-3% compared to before this series, which is within noise tolerance. Co-developed-by: Heiko Carstens Signed-off-by: Heiko Carstens Signed-off-by: Andrew Donnellan --- The way I've implemented this, I do the check between vcpu_pre_run() and entering the guest, and bail out of the loop if kvm_xfer_to_guest_mode_handle_work() returns nonzero, without calling vcpu_post_run(). My impression is that this is safe, but it does mean there is an sie_enter vcpu event and trace event which isn't matched with corresponding exit events. Is this a problem? --- arch/s390/kvm/Kconfig | 1 + arch/s390/kvm/kvm-s390.c | 25 ++++++++++++++++++------- arch/s390/kvm/vsie.c | 17 ++++++++++++----- 3 files changed, 31 insertions(+), 12 deletions(-) diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig index cae908d645501ef7eb4edbe87b8431f6499370a4..0ca9d6587243c98034d086c0ebd= 4ef085e504faf 100644 --- a/arch/s390/kvm/Kconfig +++ b/arch/s390/kvm/Kconfig @@ -30,6 +30,7 @@ config KVM select HAVE_KVM_NO_POLL select KVM_VFIO select MMU_NOTIFIER + select VIRT_XFER_TO_GUEST_WORK help Support hosting paravirtualized guest machines using the SIE virtualization capability on the mainframe. This should work diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 3cad08662b3d80aaf6f5f8891fc08b383c3c44d4..759158695bcdbb7c96c9708b2c7= 529d6e4484304 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -14,6 +14,7 @@ #define pr_fmt(fmt) KMSG_COMPONENT ": " fmt =20 #include +#include #include #include #include @@ -4788,9 +4789,6 @@ static int vcpu_pre_run(struct kvm_vcpu *vcpu) vcpu->arch.sie_block->gg14 =3D vcpu->run->s.regs.gprs[14]; vcpu->arch.sie_block->gg15 =3D vcpu->run->s.regs.gprs[15]; =20 - if (need_resched()) - schedule(); - if (!kvm_is_ucontrol(vcpu->kvm)) { rc =3D kvm_s390_deliver_pending_interrupts(vcpu); if (rc || guestdbg_exit_pending(vcpu)) @@ -5095,12 +5093,12 @@ static int __vcpu_run(struct kvm_vcpu *vcpu) */ kvm_vcpu_srcu_read_lock(vcpu); =20 - do { + while (true) { rc =3D vcpu_pre_run(vcpu); + kvm_vcpu_srcu_read_unlock(vcpu); if (rc || guestdbg_exit_pending(vcpu)) break; =20 - kvm_vcpu_srcu_read_unlock(vcpu); /* * As PF_VCPU will be used in fault handler, between * guest_timing_enter_irqoff and guest_timing_exit_irqoff @@ -5113,6 +5111,16 @@ static int __vcpu_run(struct kvm_vcpu *vcpu) } =20 local_irq_disable(); + + xfer_to_guest_mode_prepare(); + if (xfer_to_guest_mode_work_pending()) { + local_irq_enable(); + rc =3D kvm_xfer_to_guest_mode_handle_work(vcpu); + if (rc) + break; + local_irq_disable(); + } + guest_timing_enter_irqoff(); __disable_cpu_timer_accounting(vcpu); =20 @@ -5142,9 +5150,12 @@ static int __vcpu_run(struct kvm_vcpu *vcpu) kvm_vcpu_srcu_read_lock(vcpu); =20 rc =3D vcpu_post_run(vcpu, exit_reason); - } while (!signal_pending(current) && !guestdbg_exit_pending(vcpu) && !rc); + if (rc || guestdbg_exit_pending(vcpu)) { + kvm_vcpu_srcu_read_unlock(vcpu); + break; + } + }; =20 - kvm_vcpu_srcu_read_unlock(vcpu); return rc; } =20 diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c index 347268f89f2f186bea623a3adff7376cabc305b2..3a5219d0587343c2d0ea17adff3= 56ad3284a5f33 100644 --- a/arch/s390/kvm/vsie.c +++ b/arch/s390/kvm/vsie.c @@ -1181,11 +1181,21 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struc= t vsie_page *vsie_page) barrier(); if (!kvm_s390_vcpu_sie_inhibited(vcpu)) { local_irq_disable(); + xfer_to_guest_mode_prepare(); + if (xfer_to_guest_mode_work_pending()) { + local_irq_enable(); + rc =3D kvm_xfer_to_guest_mode_handle_work(vcpu); + if (rc) + goto skip_sie; + local_irq_disable(); + } guest_timing_enter_irqoff(); rc =3D kvm_s390_enter_exit_sie(scb_s, vcpu->run->s.regs.gprs, vsie_page-= >gmap->asce); guest_timing_exit_irqoff(); local_irq_enable(); } + +skip_sie: barrier(); vcpu->arch.sie_block->prog0c &=3D ~PROG_IN_SIE; =20 @@ -1345,13 +1355,11 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct v= sie_page *vsie_page) * but rewind the PSW to re-enter SIE once that's completed * instead of passing a "no action" intercept to the guest. */ - if (signal_pending(current) || - kvm_s390_vcpu_has_irq(vcpu, 0) || + if (kvm_s390_vcpu_has_irq(vcpu, 0) || kvm_s390_vcpu_sie_inhibited(vcpu)) { kvm_s390_rewind_psw(vcpu, 4); break; } - cond_resched(); } =20 if (rc =3D=3D -EFAULT) { @@ -1483,8 +1491,7 @@ int kvm_s390_handle_vsie(struct kvm_vcpu *vcpu) if (unlikely(scb_addr & 0x1ffUL)) return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION); =20 - if (signal_pending(current) || kvm_s390_vcpu_has_irq(vcpu, 0) || - kvm_s390_vcpu_sie_inhibited(vcpu)) { + if (kvm_s390_vcpu_has_irq(vcpu, 0) || kvm_s390_vcpu_sie_inhibited(vcpu)) { kvm_s390_rewind_psw(vcpu, 4); return 0; } --=20 2.52.0