Subject: Re: [PATCH v2] powerpc/rtas: Keep MSR[RI] set when calling RTAS

From: Nicholas Piggin <[email-masked]>
Date: Wed, 13 Apr 2022 15:58:42 +1000

Excerpts from Laurent Dufour's message of April 2, 2022 12:06 am:
> 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.
> 
> RTAS is expected to be called with MSR[RI] as specified in PAPR+ section
> "7.2.1 Machine State":
> 
>  R1–7.2.1–9. If called with MSR[RI] equal to 1, then RTAS must protect its
>  own critical regions from recursion by setting the MSRRI bit to 0 when in
>  the critical regions.
> 
> 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 patch has been tested on the following machines:
> Power KVM Guest
>   P8 S822L (host Ubuntu kernel 5.11.0-49-generic)
> PowerVM LPAR
>   P8 9119-MME (FW860.A1)
>   p9 9008-22L (FW950.00)
>   P10 9080-HEX (FW1010.00)
> 
> Changes in V2:
>  - Change comment in code to indicate NMI (Nick's comment)
>  - Add reference to PAPR+ in the change log (Michael's comment)
> 
> Cc: [email-masked]
> Suggested-by: Nicholas Piggin <[email-masked]>
> Signed-off-by: Laurent Dufour <[email-masked]>

Still looks good,

Reviewed-by: Nicholas Piggin <[email-masked]>

> ---
>  arch/powerpc/kernel/entry_64.S | 20 ++++++++------------
>  arch/powerpc/kernel/rtas.c     |  5 +++++
>  2 files changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index 9581906b5ee9..65cb14b56f8d 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -330,22 +330,18 @@ _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 let MSR[]RI on as we may hit
> +	 * NMI (SRESET or MCE). RTAS should disable RI in its critical
> +	 * regions (as specified in PAPR+ section 7.2.1). */
> +	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
> 
>