Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <8e3175ff-afba-e2a2-4fe6-0f964da0fa4b@linux.ibm.com>
Date:   Tue, 29 Mar 2022 10:50:59 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0)
 Gecko/20100101 Thunderbird/91.7.0
Subject: Re: [PATCH] powerpc/rtas: Keep MSR RI set when calling RTAS
Content-Language: en-US
To:     Nicholas Piggin <npiggin@gmail.com>, mpe@ellerman.id.au
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        stable@vger.kernel.org
References: <20220317110601.86917-1-ldufour@linux.ibm.com>
 <1648542633.wzscjm967w.astroid@bobo.none>
From:   Laurent Dufour <ldufour@linux.ibm.com>
In-Reply-To: <1648542633.wzscjm967w.astroid@bobo.none>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 29/03/2022, 10:31:33, Nicholas Piggin wrote:
> Excerpts from Laurent Dufour's message of March 17, 2022 9:06 pm:
>> RTAS runs in real mode (MSR[DR] and MSR[IR] unset) and in 32bits
>> mode (MSR[SF] unset).
>>
>> The change in MSR is done in enter_rtas() in a relatively complex way,
>> since the MSR value could be hardcoded.
>>
>> Furthermore, a panic has been reported when hitting the watchdog interrupt
>> while running in RTAS, this leads to the following stack trace:
>>
>> [69244.027433][   C24] watchdog: CPU 24 Hard LOCKUP
>> [69244.027442][   C24] watchdog: CPU 24 TB:997512652051031, last heartbeat TB:997504470175378 (15980ms ago)
>> [69244.027451][   C24] Modules linked in: chacha_generic(E) libchacha(E) xxhash_generic(E) wp512(E) sha3_generic(E) rmd160(E) poly1305_generic(E) libpoly1305(E) michael_mic(E) md4(E) crc32_generic(E) cmac(E) ccm(E) algif_rng(E) twofish_generic(E) twofish_common(E) serpent_generic(E) fcrypt(E) des_generic(E) libdes(E) cast6_generic(E) cast5_generic(E) cast_common(E) camellia_generic(E) blowfish_generic(E) blowfish_common(E) algif_skcipher(E) algif_hash(E) gcm(E) algif_aead(E) af_alg(E) tun(E) rpcsec_gss_krb5(E) auth_rpcgss(E)
>> nfsv4(E) dns_resolver(E) rpadlpar_io(EX) rpaphp(EX) xsk_diag(E) tcp_diag(E) udp_diag(E) raw_diag(E) inet_diag(E) unix_diag(E) af_packet_diag(E) netlink_diag(E) nfsv3(E) nfs_acl(E) nfs(E) lockd(E) grace(E) sunrpc(E) fscache(E) netfs(E) af_packet(E) rfkill(E) bonding(E) tls(E) ibmveth(EX) crct10dif_vpmsum(E) rtc_generic(E) drm(E) drm_panel_orientation_quirks(E) fuse(E) configfs(E) backlight(E) ip_tables(E) x_tables(E) dm_service_time(E) sd_mod(E) t10_pi(E)
>> [69244.027555][   C24]  ibmvfc(EX) scsi_transport_fc(E) vmx_crypto(E) gf128mul(E) btrfs(E) blake2b_generic(E) libcrc32c(E) crc32c_vpmsum(E) xor(E) raid6_pq(E) dm_mirror(E) dm_region_hash(E) dm_log(E) sg(E) dm_multipath(E) dm_mod(E) scsi_dh_rdac(E) scsi_dh_emc(E) scsi_dh_alua(E) scsi_mod(E)
>> [69244.027587][   C24] Supported: No, Unreleased kernel
>> [69244.027600][   C24] CPU: 24 PID: 87504 Comm: drmgr Kdump: loaded Tainted: G            E  X    5.14.21-150400.71.1.bz196362_2-default #1 SLE15-SP4 (unreleased) 0d821077ef4faa8dfaf370efb5fdca1fa35f4e2c
>> [69244.027609][   C24] NIP:  000000001fb41050 LR: 000000001fb4104c CTR: 0000000000000000
>> [69244.027612][   C24] REGS: c00000000fc33d60 TRAP: 0100   Tainted: G            E  X     (5.14.21-150400.71.1.bz196362_2-default)
>> [69244.027615][   C24] MSR:  8000000002981000 <SF,VEC,VSX,ME>  CR: 48800002  XER: 20040020
>> [69244.027625][   C24] CFAR: 000000000000011c IRQMASK: 1
>> [69244.027625][   C24] GPR00: 0000000000000003 ffffffffffffffff 0000000000000001 00000000000050dc
>> [69244.027625][   C24] GPR04: 000000001ffb6100 0000000000000020 0000000000000001 000000001fb09010
>> [69244.027625][   C24] GPR08: 0000000020000000 0000000000000000 0000000000000000 0000000000000000
>> [69244.027625][   C24] GPR12: 80040000072a40a8 c00000000ff8b680 0000000000000007 0000000000000034
>> [69244.027625][   C24] GPR16: 000000001fbf6e94 000000001fbf6d84 000000001fbd1db0 000000001fb3f008
>> [69244.027625][   C24] GPR20: 000000001fb41018 ffffffffffffffff 000000000000017f fffffffffffff68f
>> [69244.027625][   C24] GPR24: 000000001fb18fe8 000000001fb3e000 000000001fb1adc0 000000001fb1cf40
>> [69244.027625][   C24] GPR28: 000000001fb26000 000000001fb460f0 000000001fb17f18 000000001fb17000
>> [69244.027663][   C24] NIP [000000001fb41050] 0x1fb41050
>> [69244.027696][   C24] LR [000000001fb4104c] 0x1fb4104c
>> [69244.027699][   C24] Call Trace:
>> [69244.027701][   C24] Instruction dump:
>> [69244.027723][   C24] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
>> [69244.027728][   C24] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
>> [69244.027762][T87504] Oops: Unrecoverable System Reset, sig: 6 [#1]
>> [69244.028044][T87504] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
>> [69244.028089][T87504] Modules linked in: chacha_generic(E) libchacha(E) xxhash_generic(E) wp512(E) sha3_generic(E) rmd160(E) poly1305_generic(E) libpoly1305(E) michael_mic(E) md4(E) crc32_generic(E) cmac(E) ccm(E) algif_rng(E) twofish_generic(E) twofish_common(E) serpent_generic(E) fcrypt(E) des_generic(E) libdes(E) cast6_generic(E) cast5_generic(E) cast_common(E) camellia_generic(E) blowfish_generic(E) blowfish_common(E) algif_skcipher(E) algif_hash(E) gcm(E) algif_aead(E) af_alg(E) tun(E) rpcsec_gss_krb5(E) auth_rpcgss(E)
>> nfsv4(E) dns_resolver(E) rpadlpar_io(EX) rpaphp(EX) xsk_diag(E) tcp_diag(E) udp_diag(E) raw_diag(E) inet_diag(E) unix_diag(E) af_packet_diag(E) netlink_diag(E) nfsv3(E) nfs_acl(E) nfs(E) lockd(E) grace(E) sunrpc(E) fscache(E) netfs(E) af_packet(E) rfkill(E) bonding(E) tls(E) ibmveth(EX) crct10dif_vpmsum(E) rtc_generic(E) drm(E) drm_panel_orientation_quirks(E) fuse(E) configfs(E) backlight(E) ip_tables(E) x_tables(E) dm_service_time(E) sd_mod(E) t10_pi(E)
>> [69244.028171][T87504]  ibmvfc(EX) scsi_transport_fc(E) vmx_crypto(E) gf128mul(E) btrfs(E) blake2b_generic(E) libcrc32c(E) crc32c_vpmsum(E) xor(E) raid6_pq(E) dm_mirror(E) dm_region_hash(E) dm_log(E) sg(E) dm_multipath(E) dm_mod(E) scsi_dh_rdac(E) scsi_dh_emc(E) scsi_dh_alua(E) scsi_mod(E)
>> [69244.028307][T87504] Supported: No, Unreleased kernel
>> [69244.028385][T87504] CPU: 24 PID: 87504 Comm: drmgr Kdump: loaded Tainted: G            E  X    5.14.21-150400.71.1.bz196362_2-default #1 SLE15-SP4 (unreleased) 0d821077ef4faa8dfaf370efb5fdca1fa35f4e2c
>> [69244.028408][T87504] NIP:  000000001fb41050 LR: 000000001fb4104c CTR: 0000000000000000
>> [69244.028418][T87504] REGS: c00000000fc33d60 TRAP: 0100   Tainted: G            E  X     (5.14.21-150400.71.1.bz196362_2-default)
>> [69244.028429][T87504] MSR:  8000000002981000 <SF,VEC,VSX,ME>  CR: 48800002  XER: 20040020
>> [69244.028444][T87504] CFAR: 000000000000011c IRQMASK: 1
>> [69244.028444][T87504] GPR00: 0000000000000003 ffffffffffffffff 0000000000000001 00000000000050dc
>> [69244.028444][T87504] GPR04: 000000001ffb6100 0000000000000020 0000000000000001 000000001fb09010
>> [69244.028444][T87504] GPR08: 0000000020000000 0000000000000000 0000000000000000 0000000000000000
>> [69244.028444][T87504] GPR12: 80040000072a40a8 c00000000ff8b680 0000000000000007 0000000000000034
>> [69244.028444][T87504] GPR16: 000000001fbf6e94 000000001fbf6d84 000000001fbd1db0 000000001fb3f008
>> [69244.028444][T87504] GPR20: 000000001fb41018 ffffffffffffffff 000000000000017f fffffffffffff68f
>> [69244.028444][T87504] GPR24: 000000001fb18fe8 000000001fb3e000 000000001fb1adc0 000000001fb1cf40
>> [69244.028444][T87504] GPR28: 000000001fb26000 000000001fb460f0 000000001fb17f18 000000001fb17000
>> [69244.028534][T87504] NIP [000000001fb41050] 0x1fb41050
>> [69244.028543][T87504] LR [000000001fb4104c] 0x1fb4104c
>> [69244.028549][T87504] Call Trace:
>> [69244.028554][T87504] Instruction dump:
>> [69244.028561][T87504] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
>> [69244.028575][T87504] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
>> [69244.028607][T87504] ---[ end trace 3ddec07f638c34a2 ]---
>>
>> This happens because MSR[RI] is unset when entering RTAS but there is no
>> valid reason to not set it here.
>>
>> Fixing this by reviewing the way MSR is compute before calling RTAS. Now a
>> hardcoded value meaning real mode, 32 bits and Recoverable Interrupt is
>> loaded.
>>
>> In addition a check is added in do_enter_rtas() to detect calls made with
>> MSR[RI] unset, as we are forcing it on later.
> 
> This looks okay to me, I would just adjust the comment about watchdog
> irq. It's more like NMI (SRESET or MCE), watchdog irq could be confusing 
> for the soft-NMI timer.
> 
> Otherwise I think it's okay.
> 
> Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

Thanks Nick,

I agree about comment watchdog irq.
Michael, could you fix that comment below when applying?

> 
>>
>> Cc: stable@vger.kernel.org
>> Suggested-by: Nicholas Piggin <npiggin@gmail.com>
>> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
>> ---
>>  arch/powerpc/kernel/entry_64.S | 18 ++++++------------
>>  arch/powerpc/kernel/rtas.c     |  5 +++++
>>  2 files changed, 11 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
>> index 9581906b5ee9..fbc8dfe7da9f 100644
>> --- a/arch/powerpc/kernel/entry_64.S
>> +++ b/arch/powerpc/kernel/entry_64.S
>> @@ -330,22 +330,16 @@ _GLOBAL(enter_rtas)
>>  	clrldi	r4,r4,2			/* convert to realmode address */
>>         	mtlr	r4
>>  
>> -	li	r0,0
>> -	ori	r0,r0,MSR_EE|MSR_SE|MSR_BE|MSR_RI
>> -	andc	r0,r6,r0
>> -	
>> -        li      r9,1
>> -        rldicr  r9,r9,MSR_SF_LG,(63-MSR_SF_LG)
>> -	ori	r9,r9,MSR_IR|MSR_DR|MSR_FE0|MSR_FE1|MSR_FP|MSR_RI|MSR_LE
>> -	andc	r6,r0,r9
>> -
>>  __enter_rtas:
>> -	sync				/* disable interrupts so SRR0/1 */
>> -	mtmsrd	r0			/* don't get trashed */
>> -
>>  	LOAD_REG_ADDR(r4, rtas)
>>  	ld	r5,RTASENTRY(r4)	/* get the rtas->entry value */
>>  	ld	r4,RTASBASE(r4)		/* get the rtas->base value */
>> +
>> +	/* RTAS runs in 32bits real mode but we may hit watchdog irq */

Here I guess something like:
	/* RTAS runs in 32Bits real mode, but we may hit NMI irq */

Thanks,
Laurent.

>> +	LOAD_REG_IMMEDIATE(r6, MSR_ME|MSR_RI)
>> +
>> +	li      r0,0
>> +	mtmsrd  r0,1                    /* disable RI before using SRR0/1 */
>>  	
>>  	mtspr	SPRN_SRR0,r5
>>  	mtspr	SPRN_SRR1,r6
>> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
>> index 1f42aabbbab3..d7775b8c8853 100644
>> --- a/arch/powerpc/kernel/rtas.c
>> +++ b/arch/powerpc/kernel/rtas.c
>> @@ -49,6 +49,11 @@ void enter_rtas(unsigned long);
>>  
>>  static inline void do_enter_rtas(unsigned long args)
>>  {
>> +	unsigned long msr;
>> +
>> +	msr = mfmsr();
>> +	BUG_ON(!(msr & MSR_RI));
>> +
>>  	enter_rtas(args);
>>  
>>  	srr_regs_clobbered(); /* rtas uses SRRs, invalidate */
>> -- 
>> 2.35.1
>>
>>