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Mon, 6 Jul 2026 11:17:03 +0000 (GMT) Message-ID: <8239c9ba-154c-4e2d-b2fc-700ba12eb585@linux.ibm.com> Date: Mon, 6 Jul 2026 13:17:02 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 19/27] s390: Introduce Start Arm Execution instruction To: Steffen Eiden , kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Cc: Alexander Gordeev , Andreas Grapentin , Arnd Bergmann , Catalin Marinas , Christian Borntraeger , Claudio Imbrenda , David Hildenbrand , Friedrich Welter , Gautam Gala , Hariharan Mari , Heiko Carstens , Hendrik Brueckner , Ilya Leoshkevich , Joey Gouly , Marc Zyngier , Nico Boehr , Nina Schoetterl-Glausch , Oliver Upton , Paolo Bonzini , Suzuki K Poulose , Sven Schnelle , Ulrich Weigand , Vasily Gorbik , Will Deacon , Zenghui Yu References: <20260706085229.979525-1-seiden@linux.ibm.com> <20260706085229.979525-20-seiden@linux.ibm.com> Content-Language: en-US From: Janosch Frank Autocrypt: addr=frankja@linux.ibm.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA2MDEwOSBTYWx0ZWRfX+xIhLAcxsHLZ f9Rbt2L9sMzlOlmiuaBV/trvtk8Anz1boO8La5Yq1tJHC7H3MZNacc8bOMQw6jP++eds89zWf1c MEgJALXgnggU4S1OJ4pEZm3L8/U61oY= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA2MDEwOSBTYWx0ZWRfX9ItXXrPx0Eho MmApuRdym0zu+BWxo5RNN6GkY8w39oZAbnexTdQm5nGWemvBHbHTn5ImhU2uxdbIc640QO5JJ7S ORDTZyxBetxbGjI5rDL6iT/JkykMuxpAUtzyMnd7pNyRzmFGoqDM5vJRsSsndrF7X5NLKBKiF2n 9ULgONVX3kTRr7wZiasCa/Kj7lBgGRD5nW3HJ3wS9sk+nCETJqKjTUjcKtVn/3QfZXX8f7dNQXD tr3EIOr6166Qmd7FaYHAaPvo5kCZsgHHn/h1Sh/9EExEw8O2mn1dZBpAs+C+UUM3C6MbneotCpS Jirktf+vB3gWVsMQfPho5GS5qVJGDnzM183J3nrsSOJFbdLH0CcnnPZ6odYjkHAcCx618puJT56 jDTuaCF8qHvJmkcrAS53tFsaf+Wcq9ul8sq7GFuiioaqIfaNg2+GetOhOi+oidUSzpRLpzoP+hC KlkAjUufKmO3Yyhl/Pg== X-Proofpoint-GUID: osnHUPaW3GcYLybZTEv5viafEL5-tZh3 X-Authority-Analysis: v=2.4 cv=Oot/DS/t c=1 sm=1 tr=0 ts=6a4b8eb8 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=yZFHy3xYVWHLONAxsiAA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: osnHUPaW3GcYLybZTEv5viafEL5-tZh3 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-07-06_01,2026-07-03_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 lowpriorityscore=0 clxscore=1015 impostorscore=0 phishscore=0 malwarescore=0 suspectscore=0 spamscore=0 adultscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607060109 On 7/6/26 10:52, Steffen Eiden wrote: > The Start Arm Execution (SAE) instruction is the centerpiece for > executing arm64 (KVM) guests on s390. Its purpose is, similar to SIE, to > enable accelerated execution of arm64 virtual machines. SAE expects the > physical address of a control block as the only argument. > > The host is responsible to save & restore > - GPRs 0-13 > - access register 0-15 > - breaking event register (BEAR) > - vector/floating point registers > between SAE executions to guarantee host consistency. > > GPRs and BEAR are save and restores in the asm functions. The other > register are handled in within C code. Access registers are handled in a > later patch and SVEs will be handled when they are introduced in a > future series. Most arm64 registers are handled by a satellite block > called save_area. Some registers, frequently used by hypervisors, are > placed into the SAE control block itself. > > Enlighten asm/kvm_host_types.h for the new header variant. The new > header is chosen instead of asm/kvm_host_s390_types.h if KVM_S390_ARM64 > is defined. > [...] > + u64 gpr[31]; /* 0x0300 */ > + u64 _03f8; /* 0x03f8 */ > + > + union { > + u64 icptd[8]; /* 0x0400 */ > + /* validity-interception reason; icptr 0x01 */ > +#define SAE_VIR_UNKNOWN 0x00 > +#define SAE_VIR_UNSUPP_FORMAT 0x01 > +#define SAE_VIR_MSO_BOUNDS 0x02 > +#define SAE_VIR_MSLA 0x03 > +#define SAE_VIR_MGPAS 0x04 > +#define SAE_VIR_INVAL_SYSREG 0x05 > +#define SAE_VIR_HOST_CONTROL 0x06 > +#define SAE_VIR_SCA 0x07 > +#define SAE_VIR_MSO_ALIGN 0x08 > +#define SAE_VIR_HLC 0x09 > +#define SAE_VIR_IRPTC 0x0a Will these ever be used for something? > + u16 vir; /* 0x0400 */ > + /* host access interception details; icptr 0x02 */ > + struct { > + u64 esr_elz; /* 0x0400 */ > + u8 _0408[6]; /* 0x0408 */ > + u16 pic; /* 0x040e */ > + union teid teid; /* 0x0410 */ > + gva_t far_elz; /* 0x0418 */ > + gva_t vaddr; /* 0x0420 */ > + u64 suppl; /* 0x0428 */ > + u8 gltl; /* 0x0430 */ > + u8 _0431[7]; /* 0x0431 */ > + u64 _0438; /* 0x0438 */ > + } hai; > + /* exception-interception details; icptr 0x03 */ > + struct { > + u64 esr_elz; /* 0x0400 */ > + u64 _0408[2]; /* 0x0408 */ > + gva_t far_elz; /* 0x0418 */ > + } trap; > + /* timer-interception reason; icptr 0x04 */ > +#define SAE_IR_TIMER_ID_VIRT BIT(6) > +#define SAE_IR_TIMER_ID_PHYS BIT(7) > + u8 tir; /* 0x0400 */ > + }; > + u64 _0440[376]; /* 0x0440 */ > +} __packed __aligned(PAGE_SIZE); > +static_assert(sizeof(struct kvm_sae_block) == PAGE_SIZE); > + [...] > +#if IS_ENABLED(CONFIG_KVM_ARM64) > +/* > + * __sae64a calling convention: > + * %r2 pointer to sae control block physical address > + */ > +SYM_FUNC_START(__sae64a) > + stmg %r6,%r14,__SF_GPRS(%r15) # store kernel registers > + STBEAR __SF_SAE_BEAR(%r15) # save breaking event address register > + .insn rre,0xb9a50000,%r2,0 # Start Arm Execution > +# Let the next instruction be NOP to avoid triggering a machine check > +# and handling it in a guest as result of the instruction execution. @Christian: I have the feeling things got lost in translation when this comment was written. How would we trigger a MCHECK by having an instruction after SIE/SAE? AFAIU this allows us to have a label which we can check in the mcheck handler to decide who triggered the mcheck. Without the label the comment and NOP are useless as far as I can see. So we need to decide if this still applies and then either remove it or add sae handling to mcck_int_handler and maybe other mcheck functions. > + nopr 7 > + LBEAR __SF_SAE_BEAR(%r15) # restore breaking event address register > + lmg %r6,%r14,__SF_GPRS(%r15) # restore kernel registers > + xgr %r0,%r0 # clear guest registers to > + xgr %r1,%r1 # prevent speculative use > + xgr %r3,%r3 > + xgr %r2,%r2 > + xgr %r4,%r4 > + xgr %r5,%r5 > + BR_EX %r14 > +SYM_FUNC_END(__sae64a) > +EXPORT_SYMBOL(__sae64a) > +#endif > + > /* > * SVC interrupt handler routine. System calls are synchronous events and > * are entered with interrupts disabled. > diff --git a/arch/s390/tools/opcodes.txt b/arch/s390/tools/opcodes.txt > index def2659f6602..0e4773c94af0 100644 > --- a/arch/s390/tools/opcodes.txt > +++ b/arch/s390/tools/opcodes.txt > @@ -594,6 +594,9 @@ b9a0 clp RRF_U0RR > b9a1 tpei RRE_RR > b9a2 ptf RRE_R0 > b9a4 uvc RRF_URR > +b9a5 sae RRE_R0 > +b9a6 lasrm RRE_R0 > +b9a7 stiasrm RRE_R0 > b9aa lptea RRF_RURR2 > b9ab essa RRF_U0RR > b9ac irbm RRE_RR