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

From: Nicholas Piggin
Date: Wed Apr 13 2022 - 01:59:00 EST

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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: stable@xxxxxxxxxxxxxxx
> Suggested-by: Nicholas Piggin <npiggin@xxxxxxxxx>
> Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxx>

Still looks good,

Reviewed-by: Nicholas Piggin <npiggin@xxxxxxxxx>

> ---
> 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
>
>

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