Subject: Re: [EXT] Re: [PATCH] irqchip/gic-v3: Workaround Marvell erratum 38545 when reading IAR

From: Marc Zyngier <[email-masked]>
Date: Tue, 01 Mar 2022 15:10:03 +0000

Linu,

On Tue, 01 Mar 2022 07:13:21 +0000,
Linu Cherian <[email-masked]> wrote:
> 
> Hi Marc,
> 
> > -----Original Message-----
> > From: Marc Zyngier <[email-masked]>
> > Sent: Saturday, February 26, 2022 7:20 PM
> > To: Linu Cherian <[email-masked]>
> > Cc: [email-masked]; [email-masked]; [email-masked]; linux-
> > [email-masked]; [email-masked];
> > [email-masked]
> > Subject: [EXT] Re: [PATCH] irqchip/gic-v3: Workaround Marvell erratum
> > 38545 when reading IAR
> > 
> > External Email
> > 
> > ----------------------------------------------------------------------
> > On Sat, 26 Feb 2022 12:33:32 +0000,
> > Linu Cherian <[email-masked]> wrote:
> > >
> > > When a IAR register read races with a GIC interrupt RELEASE event,
> > > GIC-CPU interface could wrongly return a valid INTID to the CPU for an
> > > interrupt that is already released(non activated) instead of 0x3ff.
> > >
> > > As a side effect, an interrupt handler could run twice, once with
> > > interrupt priority and then with idle priority.
> > >
> > > As a workaround, gic_read_iar is updated so that it will return a
> > > valid interrupt ID only if there is a change in the active priority
> > > list after the IAR read on all the affected Silicons.
> > >
> > > Along with this, Thunderx erratum 23154 is reworked to use GIC IIDR
> > > based quirk management for the sake of consistency and also because
> > > there is workaround overlap on some silicon variants.
> > >
> > > Signed-off-by: Linu Cherian <[email-masked]>
> > > ---
> > >  Documentation/arm64/silicon-errata.rst |  4 +-
> > >  arch/arm64/Kconfig                     | 10 -----
> > >  arch/arm64/include/asm/arch_gicv3.h    | 24 +++++++++--
> > >  arch/arm64/kernel/cpu_errata.c         |  8 ----
> > >  arch/arm64/tools/cpucaps               |  1 -
> > >  drivers/irqchip/irq-gic-v3.c           | 56 +++++++++++++++++++++++++-
> > >  6 files changed, 77 insertions(+), 26 deletions(-)
> > >
> > > diff --git a/Documentation/arm64/silicon-errata.rst
> > > b/Documentation/arm64/silicon-errata.rst
> > > index ea281dd75517..f602faf4bf82 100644
> > > --- a/Documentation/arm64/silicon-errata.rst
> > > +++ b/Documentation/arm64/silicon-errata.rst
> > > @@ -136,10 +136,12 @@ stable kernels.
> > >  +----------------+-----------------+-----------------+-----------------------------+
> > >  | Cavium         | ThunderX ITS    | #23144          | CAVIUM_ERRATUM_23144
> > |
> > >
> > > +----------------+-----------------+-----------------+----------------
> > > -------------+
> > > -| Cavium         | ThunderX GICv3  | #23154          |
> > CAVIUM_ERRATUM_23154        |
> > > +| Cavium         | ThunderX GICv3  | #23154          | N/A                         |
> > >  +----------------+-----------------+-----------------+-----------------------------+
> > >  | Cavium         | ThunderX GICv3  | #38539          | N/A                         |
> > >
> > > +----------------+-----------------+-----------------+----------------
> > > -------------+
> > > +| Cavium         | ThunderX GICv3  | #38545          | N/A                         |
> > 
> > Cavium? Or Marvell? I can understand the identity crisis, but you should pick
> > your poison. It also seem to affect the new TX2 rather than (or in addition to)
> > the ancient TX.
> 
> It doesn't applies to Tx2(ThunderX2) and it affects OcteonTx2, OcteonTx
> and ThunderX.
> 
> In the V2 will rename this as OcteonTx2 to avoid confusion with ThunderX2.
> 
> 
> > 
> > > ++----------------+-----------------+-----------------+-----------------------------+
> > >  | Cavium         | ThunderX Core   | #27456          |
> > CAVIUM_ERRATUM_27456        |
> > >  +----------------+-----------------+-----------------+-----------------------------+
> > >  | Cavium         | ThunderX Core   | #30115          |
> > CAVIUM_ERRATUM_30115        |
> > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index
> > > 09b885cc4db5..889cb56bf5ec 100644
> > > --- a/arch/arm64/Kconfig
> > > +++ b/arch/arm64/Kconfig
> > > @@ -890,16 +890,6 @@ config CAVIUM_ERRATUM_23144
> > >
> > >  	  If unsure, say Y.
> > >
> > > -config CAVIUM_ERRATUM_23154
> > > -	bool "Cavium erratum 23154: Access to ICC_IAR1_EL1 is not sync'ed"
> > > -	default y
> > > -	help
> > > -	  The gicv3 of ThunderX requires a modified version for
> > > -	  reading the IAR status to ensure data synchronization
> > > -	  (access to icc_iar1_el1 is not sync'ed before and after).
> > > -
> > > -	  If unsure, say Y.
> > > -
> > 
> > This is starting really badly. Why make this config option disappear?
> > 
> > This is both useful for documentation (in the absence of a public errata
> > document from the silicon vendor, I *really* want to know what I am affected
> > by) and for people who do not want their kernels to be encumbered by
> > support for broken HW.
> > 
> > I actually want to see a description of the *new* errata in Kconfig, warts and
> > all.
> 
> 
> Ack. Will revert this.
> 
> Let me clarify the reason why it was removed. 
> IIUC, there are two ways in which errata is managed in the GIC driver.
> 1. GICD_IIDR based quirk management
> 2. CPU MIDR based quirk management
> 
> Somehow I overlooked the virtualization scenario and missed the point that, 
> GICD_IIDR doesn't reflect the actual Silicon implementer in a guest unlike CPU MIDR and 
> hence wrongly assumed that the errata will take effect in both host and guest.
>  
> Opted for the IIDR method(option #1), since it was contained within the GIC driver.
> Will change this to option #2 .
> 
> > 
> > >  config CAVIUM_ERRATUM_27456
> > >  	bool "Cavium erratum 27456: Broadcast TLBI instructions may cause
> > icache corruption"
> > >  	default y
> > > diff --git a/arch/arm64/include/asm/arch_gicv3.h
> > > b/arch/arm64/include/asm/arch_gicv3.h
> > > index 4ad22c3135db..bc98a60a4bcb 100644
> > > --- a/arch/arm64/include/asm/arch_gicv3.h
> > > +++ b/arch/arm64/include/asm/arch_gicv3.h
> > > @@ -47,21 +47,37 @@ static inline u64 gic_read_iar_common(void)
> > >  	return irqstat;
> > >  }
> > >
> > > -/*
> > > +/* Marvell Erratum 38545
> > > + *
> > > + * When a IAR register read races with a GIC interrupt RELEASE event,
> > > + * GIC-CPU interface could wrongly return a valid INTID to the CPU
> > > + * for an interrupt that is already released(non activated) instead of 0x3ff.
> > > + *
> > > + * To workaround this, return a valid interrupt ID only if there is a
> > > +change
> > > + * in the active priority list after the IAR read.
> > > + *
> > >   * Cavium ThunderX erratum 23154
> > >   *
> > >   * The gicv3 of ThunderX requires a modified version for reading the
> > >   * IAR status to ensure data synchronization (access to icc_iar1_el1
> > >   * is not sync'ed before and after).
> > > + *
> > > + * Have merged both the workarounds into a common function since,
> > > + * 1. On Thunderx 88xx 1.x both erratas are applicable.
> > 
> > This is new. Are you saying that TX is also affected by this new bug?
> > Experience doesn't seem to support this statement, but I am prepared to
> > believe that this thing is even more broken than I thought.
> > 
> 
> Yes. Thunderx is affected by this new bug as well but got identified
> only while testing on a OcteonTx2 hardware. HW team has confirmed
> that it applies to the older ThudnderX and OcteonTx Silicons as
> well.

Oh great. Copy paste strikes back... :-/

> 
> 
> > Also, what is the story for virtualisation? Does the ICV interface
> > suffer from the same bug? I can't see why not (23154 definitely
> > affects virtualisation).
> > 
> 
> Yes. It affects virtualization as well and the errata is applicable
> to ICV interface.

/me picks a spare TX SoC from the bin and frames it.

> 
> 
> > > + * 2. Having extra nops doesn't add any side effects for Silicons where
> > > + *    erratum 23154 is not applicable.
> > >   */
> > > -static inline u64 gic_read_iar_cavium_thunderx(void)
> > > +static inline u64 gic_read_iar_marvell_38545_23154(void)
> > >  {
> > > -	u64 irqstat;
> > > +	u64 irqstat, apr;
> > >
> > > +	apr = read_sysreg_s(SYS_ICC_AP1R0_EL1);
> > >  	nops(8);
> > >  	irqstat = read_sysreg_s(SYS_ICC_IAR1_EL1);
> > >  	nops(4);
> > > -	mb();
> > > +	dsb(sy);
> > 
> > mb() *is* a dsb(sy). Why the change?
> 
> Agree the change is redundant.
> 
> > 
> > > +	if (unlikely(apr == read_sysreg_s(SYS_ICC_AP1R0_EL1)))
> > > +		return 0x3ff;
> > 
> > So you are adding extra overhead to all TX platforms that did not
> > require it.  Why is that an acceptable outcome? If all platforms
> > affected by 23154 are also affected by 38545, why are they treated
> > independently with separate flags?
> > 
> 
> Basically we need two IAR workaround functions,
> 
> #1 That takes care of both both 38545 and 23154 (For example
> #ThunderX 88xx 1.x)
> 
> #2. That cares of only 38545 
> 
> Since the only difference between the two is  12 NOPs, tried to use a
> a common function for both the workaround to avoid code duplication.
> 
> Yeah. Agree that separate flags were really not required.
> 
> Will keep #1 and #2 as separate functions if that is preferred.

Maybe not. Given that hardly anyone has access to OTX2, and that there
is a gazillion of TX in the wild, the single function looks like the
right thing to do, with a single static key for both of them.

You can simply extend the current 23154 workaround to also take care
of 38545 (documenting it whilst you're at it), and the patch should be
10 lines at most.

> 
> 
> > >
> > >  	return irqstat;
> > >  }
> > > diff --git a/arch/arm64/kernel/cpu_errata.c
> > > b/arch/arm64/kernel/cpu_errata.c index b217941713a8..79beb800ee79
> > > 100644
> > > --- a/arch/arm64/kernel/cpu_errata.c
> > > +++ b/arch/arm64/kernel/cpu_errata.c
> > > @@ -423,14 +423,6 @@ const struct arm64_cpu_capabilities
> > arm64_errata[] = {
> > >  		ERRATA_MIDR_RANGE_LIST(erratum_845719_list),
> > >  	},
> > >  #endif
> > > -#ifdef CONFIG_CAVIUM_ERRATUM_23154
> > > -	{
> > > -	/* Cavium ThunderX, pass 1.x */
> > > -		.desc = "Cavium erratum 23154",
> > > -		.capability = ARM64_WORKAROUND_CAVIUM_23154,
> > > -		ERRATA_MIDR_REV_RANGE(MIDR_THUNDERX, 0, 0, 1),

Expand this to an MIDR list instead of a single range in order to
handle OTX2 as well.

> > > -	},
> > > -#endif
> > 
> > NAK. See below.
> > 
> > >  #ifdef CONFIG_CAVIUM_ERRATUM_27456
> > >  	{
> > >  		.desc = "Cavium erratum 27456",
> > > diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps index
> > > 9c65b1e25a96..3f751fe4fec4 100644
> > > --- a/arch/arm64/tools/cpucaps
> > > +++ b/arch/arm64/tools/cpucaps
> > > @@ -62,7 +62,6 @@ WORKAROUND_2077057
> > >  WORKAROUND_TRBE_OVERWRITE_FILL_MODE
> > >  WORKAROUND_TSB_FLUSH_FAILURE
> > >  WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> > > -WORKAROUND_CAVIUM_23154
> > >  WORKAROUND_CAVIUM_27456
> > >  WORKAROUND_CAVIUM_30115
> > >  WORKAROUND_CAVIUM_TX2_219_PRFM
> > > diff --git a/drivers/irqchip/irq-gic-v3.c
> > > b/drivers/irqchip/irq-gic-v3.c index 5e935d97207d..a3b58bf4fce4 100644
> > > --- a/drivers/irqchip/irq-gic-v3.c
> > > +++ b/drivers/irqchip/irq-gic-v3.c
> > > @@ -35,6 +35,8 @@
> > >
> > >  #define FLAGS_WORKAROUND_GICR_WAKER_MSM8996	(1ULL << 0)
> > >  #define FLAGS_WORKAROUND_CAVIUM_ERRATUM_38539	(1ULL << 1)
> > > +#define FLAGS_WORKAROUND_CAVIUM_ERRATUM_23154	(1ULL << 2)
> > > +#define FLAGS_WORKAROUND_MARVELL_ERRATUM_38545	(1ULL
> > << 3)
> > >
> > >  #define GIC_IRQ_TYPE_PARTITION	(GIC_IRQ_TYPE_LPI + 1)
> > >
> > > @@ -60,6 +62,7 @@ struct gic_chip_data {
> > >
> > >  static struct gic_chip_data gic_data __read_mostly;  static
> > > DEFINE_STATIC_KEY_TRUE(supports_deactivate_key);
> > > +static DEFINE_STATIC_KEY_FALSE(gic_iar_quirk);
> > >
> > >  #define GIC_ID_NR	(1U <<
> > GICD_TYPER_ID_BITS(gic_data.rdists.gicd_typer))
> > >  #define GIC_LINE_NR
> > 	min(GICD_TYPER_SPIS(gic_data.rdists.gicd_typer), 1020U)
> > > @@ -235,10 +238,19 @@ static void gic_redist_wait_for_rwp(void)
> > >
> > >  #ifdef CONFIG_ARM64
> > >
> > > +static u64 __maybe_unused gic_read_iar_fixup(void) {
> > > +	if (gic_data.flags &
> > FLAGS_WORKAROUND_MARVELL_ERRATUM_38545 ||
> > > +		gic_data.flags &
> > FLAGS_WORKAROUND_CAVIUM_ERRATUM_23154)
> > > +		return gic_read_iar_marvell_38545_23154();
> > > +	else /* Not possible */
> > > +		return ICC_IAR1_EL1_SPURIOUS;
> > 
> > Not possible? What does that even mean? And what is the point of gating
> > things with a static key if you have to check again with an extra load?
> > 
> 
> Please see below.
> 
> > > +}
> > > +
> > >  static u64 __maybe_unused gic_read_iar(void)  {
> > > -	if (cpus_have_const_cap(ARM64_WORKAROUND_CAVIUM_23154))
> > > -		return gic_read_iar_cavium_thunderx();
> > > +	if (static_branch_unlikely(&gic_iar_quirk))
> > > +		return gic_read_iar_fixup();
> > 
> > You are trading a static key for another one describing... the same thing. What
> > is the point?
> 
> The real intention was to avoid an additional if check getting
> introduced like below for Silicon not affected by both of these
> errata.
> 
> If (cpus_have_const_cap(ARM64_WORKAROUND_CAVIUM23154))
> 	return gic_read_iar_38545_23154(); /* Both workaround applicable */
> else if (cpus_have_const_cap(ARM64_WORKAROUND_CAVIUM38545))
>               return gic_read_iar_38545();  /* Only 38545 applicable */
> 
> So tried to use a static key, gic_iar_quirk instead.

Nah, just key it against ARM64_WORKAROUND_CAVIUM_23154. As you pointed
out, NOPs are cheap. That will be  an incentive for someone to debug
this HW.

To sum it up, stash the actual workaround in the existing function,
and the rest as below (obviously it doesn't compile).

Thanks,

	M.

diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst
index ea281dd75517..466cb9e89047 100644
--- a/Documentation/arm64/silicon-errata.rst
+++ b/Documentation/arm64/silicon-errata.rst
@@ -136,7 +136,7 @@ stable kernels.
 +----------------+-----------------+-----------------+-----------------------------+
 | Cavium         | ThunderX ITS    | #23144          | CAVIUM_ERRATUM_23144        |
 +----------------+-----------------+-----------------+-----------------------------+
-| Cavium         | ThunderX GICv3  | #23154          | CAVIUM_ERRATUM_23154        |
+| Cavium         | ThunderX GICv3  | #23154,38545    | CAVIUM_ERRATUM_23154        |
 +----------------+-----------------+-----------------+-----------------------------+
 | Cavium         | ThunderX GICv3  | #38539          | N/A                         |
 +----------------+-----------------+-----------------+-----------------------------+
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index cbcd42decb2a..049ca0cc0525 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -890,12 +890,17 @@ config CAVIUM_ERRATUM_23144
 	  If unsure, say Y.
 
 config CAVIUM_ERRATUM_23154
-	bool "Cavium erratum 23154: Access to ICC_IAR1_EL1 is not sync'ed"
+	bool "Cavium errata 23154 and 38545: GICv3 lacks HW synchronisation"
 	default y
 	help
-	  The gicv3 of ThunderX requires a modified version for
+	  The ThunderX GICv3 implementation requires a modified version for
 	  reading the IAR status to ensure data synchronization
-	  (access to icc_iar1_el1 is not sync'ed before and after).
+	  (access to icc_iar1_el1 is not sync'ed before and after, erratum
+	  23154).
+
+	  It also suffers from erratum 38545 (also present on Marvell's
+	  OcteonTX2), resulting in deactivated interrupts being spuriously
+	  presented to the CPU interface.
 
 	  If unsure, say Y.
 
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index b217941713a8..553a72b517af 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -214,6 +214,16 @@ static const struct arm64_cpu_capabilities arm64_repeat_tlbi_list[] = {
 };
 #endif
 
+#ifdef CONFIG_CAVIUM_ERRATUM_23154
+const struct midr_range cavium_erratum_23154_cpus[] = {
+	/* Cavium ThunderX, pass 1.x */
+	MIDR_RANGE(MIDR_THUNDERX, 0, 0, 0, 1),
+	/* OcteonTX2 */
+	MIDR_ALL_VERSIONS(MIDR_MRVL_OCTEONTX2),
+	{},
+};
+#endif
+
 #ifdef CONFIG_CAVIUM_ERRATUM_27456
 const struct midr_range cavium_erratum_27456_cpus[] = {
 	/* Cavium ThunderX, T88 pass 1.x - 2.1 */
@@ -425,10 +435,9 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
 #endif
 #ifdef CONFIG_CAVIUM_ERRATUM_23154
 	{
-	/* Cavium ThunderX, pass 1.x */
-		.desc = "Cavium erratum 23154",
+		.desc = "Cavium errata 23154 and 38545",
 		.capability = ARM64_WORKAROUND_CAVIUM_23154,
-		ERRATA_MIDR_REV_RANGE(MIDR_THUNDERX, 0, 0, 1),
+		ERRATA_MIDR_RANGE_LIST(cavium_erratum_23154_cpus),
 	},
 #endif
 #ifdef CONFIG_CAVIUM_ERRATUM_27456

-- 
Without deviation from the norm, progress is not possible.

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