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* [PATCH v2 0/3] arm64: Dealing with VHE-only CPUs
@ 2021-03-30 17:39 Marc Zyngier
  2021-03-30 17:39 ` [PATCH v2 1/3] arm64: cpufeature: Allow early filtering of feature override Marc Zyngier
                   ` (2 more replies)
  0 siblings, 3 replies; 11+ messages in thread
From: Marc Zyngier @ 2021-03-30 17:39 UTC (permalink / raw)
  To: linux-arm-kernel
  Cc: Hector Martin, Arnd Bergmann, Mark Rutland, Will Deacon,
	Catalin Marinas, kernel-team

This short series is a rewrite of [0] after some reviewing from
Will. It simplifies the esoteric "stay at EL2" path, and move the
feature override code where it actually belongs, allowing us to tell
the user that no, nVHE isn't a thing on these system.

Additional bonus: the box can now boot without CONFIG_ARM64_VHE (and
without KVM, of course), though that's a pretty weird state.

This allows the infamous M1 to boot (tested on a M1 Mini).

Hector, feel free to pull these two patches as a preamble to the next
version of your series, though I'd expect this to go via the arm64
tree for obvious reasons.

* From v1 [1]:
  - added a comment describing the mapping various states
    the override mask/val tuple can describe
  - added a patch to prevent KVM from initialising, treating
    the lact of CONFIG_ARM64_VHE as a mismatched boot

[0] https://lore.kernel.org/r/20210304213902.83903-2-marcan@marcan.st
[1] https://lore.kernel.org/r/20210325124721.941182-1-maz@kernel.org

Marc Zyngier (3):
  arm64: cpufeature: Allow early filtering of feature override
  arm64: Cope with CPUs stuck in VHE mode
  arm64: Allow nVHE impaired CPUs to boot without CONFIG_ARM64_VHE

 arch/arm64/include/asm/cpufeature.h | 17 +++++++++++++
 arch/arm64/include/asm/virt.h       | 18 +++++++++----
 arch/arm64/kernel/cpufeature.c      |  6 +++++
 arch/arm64/kernel/head.S            | 39 ++++++++++++++++++++++++++---
 arch/arm64/kernel/hyp-stub.S        |  8 +++---
 arch/arm64/kernel/idreg-override.c  | 26 ++++++++++++++++++-
 arch/arm64/kvm/va_layout.c          |  9 +++++++
 7 files changed, 110 insertions(+), 13 deletions(-)

-- 
2.29.2


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^ permalink raw reply	[flat|nested] 11+ messages in thread

* [PATCH v2 1/3] arm64: cpufeature: Allow early filtering of feature override
  2021-03-30 17:39 [PATCH v2 0/3] arm64: Dealing with VHE-only CPUs Marc Zyngier
@ 2021-03-30 17:39 ` Marc Zyngier
  2021-04-08 11:13   ` Hector Martin
  2021-03-30 17:39 ` [PATCH v2 2/3] arm64: Cope with CPUs stuck in VHE mode Marc Zyngier
  2021-03-30 17:39 ` [PATCH v2 3/3] arm64: Allow nVHE impaired CPUs to boot without CONFIG_ARM64_VHE Marc Zyngier
  2 siblings, 1 reply; 11+ messages in thread
From: Marc Zyngier @ 2021-03-30 17:39 UTC (permalink / raw)
  To: linux-arm-kernel
  Cc: Hector Martin, Arnd Bergmann, Mark Rutland, Will Deacon,
	Catalin Marinas, kernel-team

Some CPUs are broken enough that some overrides need to be rejected
at the earliest opportunity. In some cases, that's right at cpu
feature override time.

Provide the necessary infrastructure to filter out overrides,
and to report such filtered out overrides to the core cpufeature code.

Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/cpufeature.h | 17 +++++++++++++++++
 arch/arm64/kernel/cpufeature.c      |  6 ++++++
 arch/arm64/kernel/idreg-override.c  | 13 +++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 61177bac49fa..fac0310cdec4 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -63,6 +63,23 @@ struct arm64_ftr_bits {
 	s64		safe_val; /* safe value for FTR_EXACT features */
 };
 
+/*
+ * Describe the early feature override to the core override code:
+ *
+ * @val			Values that are to be merged into the final
+ *			sanitised value of the register. Only the bitfields
+ *			set to 1 in @mask are valid
+ * @mask		Mask of the features that are overriden by @val
+ *
+ * A @mask field set to full-1 indicates that the corresponding field
+ * in @val is a valid override.
+ *
+ * A @mask field set to full-0 with the corresponding @val field set
+ * to full-0 denotes that this field has no override
+ *
+ * A @mask field set to full-0 with the corresponding @val field set
+ * to full-1 denotes thath this field has an invalid override.
+ */
 struct arm64_ftr_override {
 	u64		val;
 	u64		mask;
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 066030717a4c..6de15deaa912 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -809,6 +809,12 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
 					reg->name,
 					ftrp->shift + ftrp->width - 1,
 					ftrp->shift, str, tmp);
+		} else if ((ftr_mask & reg->override->val) == ftr_mask) {
+			reg->override->val &= ~ftr_mask;
+			pr_warn("%s[%d:%d]: impossible override, ignored\n",
+				reg->name,
+				ftrp->shift + ftrp->width - 1,
+				ftrp->shift);
 		}
 
 		val = arm64_ftr_set_value(ftrp, val, ftr_new);
diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index 83f1c4b92095..be92fcd319a1 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c
@@ -25,6 +25,7 @@ struct ftr_set_desc {
 	struct {
 		char			name[FTR_DESC_FIELD_LEN];
 		u8			shift;
+		bool			(*filter)(u64 val);
 	} 				fields[];
 };
 
@@ -124,6 +125,18 @@ static void __init match_options(const char *cmdline)
 			if (find_field(cmdline, regs[i], f, &v))
 				continue;
 
+			/*
+			 * If an override gets filtered out, advertise
+			 * it by setting the value to 0xf, but
+			 * clearing the mask... Yes, this is fragile.
+			 */
+			if (regs[i]->fields[f].filter &&
+			    !regs[i]->fields[f].filter(v)) {
+				regs[i]->override->val  |= mask;
+				regs[i]->override->mask &= ~mask;
+				continue;
+			}
+
 			regs[i]->override->val  &= ~mask;
 			regs[i]->override->val  |= (v << shift) & mask;
 			regs[i]->override->mask |= mask;
-- 
2.29.2


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^ permalink raw reply	[flat|nested] 11+ messages in thread

* [PATCH v2 2/3] arm64: Cope with CPUs stuck in VHE mode
  2021-03-30 17:39 [PATCH v2 0/3] arm64: Dealing with VHE-only CPUs Marc Zyngier
  2021-03-30 17:39 ` [PATCH v2 1/3] arm64: cpufeature: Allow early filtering of feature override Marc Zyngier
@ 2021-03-30 17:39 ` Marc Zyngier
  2021-04-07 21:16   ` Will Deacon
  2021-03-30 17:39 ` [PATCH v2 3/3] arm64: Allow nVHE impaired CPUs to boot without CONFIG_ARM64_VHE Marc Zyngier
  2 siblings, 1 reply; 11+ messages in thread
From: Marc Zyngier @ 2021-03-30 17:39 UTC (permalink / raw)
  To: linux-arm-kernel
  Cc: Hector Martin, Arnd Bergmann, Mark Rutland, Will Deacon,
	Catalin Marinas, kernel-team

It seems that the CPUs part of the SoC known as Apple M1 have the
terrible habit of being stuck with HCR_EL2.E2H==1, in violation
of the architecture.

Try and work around this deplorable state of affairs by detecting
the stuck bit early and short-circuit the nVHE dance. Additional
filtering code ensures that attempts at switching to nVHE from
the command-line are also ignored.

It is still unknown whether there are many more such nuggets
to be found...

Reported-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kernel/head.S           | 39 +++++++++++++++++++++++++++---
 arch/arm64/kernel/hyp-stub.S       |  8 +++---
 arch/arm64/kernel/idreg-override.c | 13 +++++++++-
 3 files changed, 52 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 840bda1869e9..96873dfa67fd 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -477,14 +477,13 @@ EXPORT_SYMBOL(kimage_vaddr)
  * booted in EL1 or EL2 respectively.
  */
 SYM_FUNC_START(init_kernel_el)
-	mov_q	x0, INIT_SCTLR_EL1_MMU_OFF
-	msr	sctlr_el1, x0
-
 	mrs	x0, CurrentEL
 	cmp	x0, #CurrentEL_EL2
 	b.eq	init_el2
 
 SYM_INNER_LABEL(init_el1, SYM_L_LOCAL)
+	mov_q	x0, INIT_SCTLR_EL1_MMU_OFF
+	msr	sctlr_el1, x0
 	isb
 	mov_q	x0, INIT_PSTATE_EL1
 	msr	spsr_el1, x0
@@ -504,9 +503,43 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL)
 	msr	vbar_el2, x0
 	isb
 
+	/*
+	 * Fruity CPUs seem to have HCR_EL2.E2H set to RES1,
+	 * making it impossible to start in nVHE mode. Is that
+	 * compliant with the architecture? Absolutely not!
+	 */
+	mrs	x0, hcr_el2
+	and	x0, x0, #HCR_E2H
+	cbz	x0, 1f
+
+	/* Switching to VHE requires a sane SCTLR_EL1 as a start */
+	mov_q	x0, INIT_SCTLR_EL1_MMU_OFF
+	msr_s	SYS_SCTLR_EL12, x0
+
+	/*
+	 * Force an eret into a helper "function", and let it return
+	 * to our original caller... This makes sure that we have
+	 * initialised the basic PSTATE state.
+	 */
+	mov	x0, #INIT_PSTATE_EL2
+	msr	spsr_el1, x0
+	adr	x0, __cpu_stick_to_vhe
+	msr	elr_el1, x0
+	eret
+
+1:
+	mov_q	x0, INIT_SCTLR_EL1_MMU_OFF
+	msr	sctlr_el1, x0
+
 	msr	elr_el2, lr
 	mov	w0, #BOOT_CPU_MODE_EL2
 	eret
+
+__cpu_stick_to_vhe:
+	mov	x0, #HVC_VHE_RESTART
+	hvc	#0
+	mov	x0, #BOOT_CPU_MODE_EL2
+	ret
 SYM_FUNC_END(init_kernel_el)
 
 /*
diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
index 5eccbd62fec8..9c9b4d8fc395 100644
--- a/arch/arm64/kernel/hyp-stub.S
+++ b/arch/arm64/kernel/hyp-stub.S
@@ -27,12 +27,12 @@ SYM_CODE_START(__hyp_stub_vectors)
 	ventry	el2_fiq_invalid			// FIQ EL2t
 	ventry	el2_error_invalid		// Error EL2t
 
-	ventry	el2_sync_invalid		// Synchronous EL2h
+	ventry	elx_sync			// Synchronous EL2h
 	ventry	el2_irq_invalid			// IRQ EL2h
 	ventry	el2_fiq_invalid			// FIQ EL2h
 	ventry	el2_error_invalid		// Error EL2h
 
-	ventry	el1_sync			// Synchronous 64-bit EL1
+	ventry	elx_sync			// Synchronous 64-bit EL1
 	ventry	el1_irq_invalid			// IRQ 64-bit EL1
 	ventry	el1_fiq_invalid			// FIQ 64-bit EL1
 	ventry	el1_error_invalid		// Error 64-bit EL1
@@ -45,7 +45,7 @@ SYM_CODE_END(__hyp_stub_vectors)
 
 	.align 11
 
-SYM_CODE_START_LOCAL(el1_sync)
+SYM_CODE_START_LOCAL(elx_sync)
 	cmp	x0, #HVC_SET_VECTORS
 	b.ne	1f
 	msr	vbar_el2, x1
@@ -71,7 +71,7 @@ SYM_CODE_START_LOCAL(el1_sync)
 
 9:	mov	x0, xzr
 	eret
-SYM_CODE_END(el1_sync)
+SYM_CODE_END(elx_sync)
 
 // nVHE? No way! Give me the real thing!
 SYM_CODE_START_LOCAL(mutate_to_vhe)
diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index be92fcd319a1..6a8a14955fba 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c
@@ -29,11 +29,22 @@ struct ftr_set_desc {
 	} 				fields[];
 };
 
+static bool __init mmfr1_vh_filter(u64 val)
+{
+	/*
+	 * If we ever reach this point while running VHE, we're
+	 * guaranteed to be on one of these funky, VHE-stuck CPUs. If
+	 * the user was trying to force nVHE on us, proceed with
+	 * attitude adjustment.
+	 */
+	return !(is_kernel_in_hyp_mode() && val == 0);
+}
+
 static const struct ftr_set_desc mmfr1 __initconst = {
 	.name		= "id_aa64mmfr1",
 	.override	= &id_aa64mmfr1_override,
 	.fields		= {
-	        { "vh", ID_AA64MMFR1_VHE_SHIFT },
+	        { "vh", ID_AA64MMFR1_VHE_SHIFT, mmfr1_vh_filter },
 		{}
 	},
 };
-- 
2.29.2


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^ permalink raw reply	[flat|nested] 11+ messages in thread

* [PATCH v2 3/3] arm64: Allow nVHE impaired CPUs to boot without CONFIG_ARM64_VHE
  2021-03-30 17:39 [PATCH v2 0/3] arm64: Dealing with VHE-only CPUs Marc Zyngier
  2021-03-30 17:39 ` [PATCH v2 1/3] arm64: cpufeature: Allow early filtering of feature override Marc Zyngier
  2021-03-30 17:39 ` [PATCH v2 2/3] arm64: Cope with CPUs stuck in VHE mode Marc Zyngier
@ 2021-03-30 17:39 ` Marc Zyngier
  2021-04-07 21:18   ` Will Deacon
  2 siblings, 1 reply; 11+ messages in thread
From: Marc Zyngier @ 2021-03-30 17:39 UTC (permalink / raw)
  To: linux-arm-kernel
  Cc: Hector Martin, Arnd Bergmann, Mark Rutland, Will Deacon,
	Catalin Marinas, kernel-team

CPUs stuck in VHE mode need some additional care if the kernel
is compiled without CONFIG_ARM64_VHE.

Treat this case as another version of a mismatched boot, and
prevent KVM from being initialised. The machine will boot in
some bizarre state, using TPIDR_EL1 instead of TPIDR_EL2, but
otherwise be functional.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/virt.h | 18 +++++++++++++-----
 arch/arm64/kvm/va_layout.c    |  9 +++++++++
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index 7379f35ae2c6..69bc4e26aa26 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h
@@ -72,6 +72,11 @@ void __hyp_reset_vectors(void);
 
 DECLARE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
 
+static inline bool is_kernel_in_hyp_mode(void)
+{
+	return read_sysreg(CurrentEL) == CurrentEL_EL2;
+}
+
 /* Reports the availability of HYP mode */
 static inline bool is_hyp_mode_available(void)
 {
@@ -83,6 +88,10 @@ static inline bool is_hyp_mode_available(void)
 	    static_branch_likely(&kvm_protected_mode_initialized))
 		return true;
 
+	/* Catch braindead CPUs */
+	if (!IS_ENABLED(CONFIG_ARM64_VHE) && is_kernel_in_hyp_mode())
+		return false;
+
 	return (__boot_cpu_mode[0] == BOOT_CPU_MODE_EL2 &&
 		__boot_cpu_mode[1] == BOOT_CPU_MODE_EL2);
 }
@@ -98,12 +107,11 @@ static inline bool is_hyp_mode_mismatched(void)
 	    static_branch_likely(&kvm_protected_mode_initialized))
 		return false;
 
-	return __boot_cpu_mode[0] != __boot_cpu_mode[1];
-}
+	/* Catch braindead CPUs */
+	if (!IS_ENABLED(CONFIG_ARM64_VHE) && is_kernel_in_hyp_mode())
+		return true;
 
-static inline bool is_kernel_in_hyp_mode(void)
-{
-	return read_sysreg(CurrentEL) == CurrentEL_EL2;
+	return __boot_cpu_mode[0] != __boot_cpu_mode[1];
 }
 
 static __always_inline bool has_vhe(void)
diff --git a/arch/arm64/kvm/va_layout.c b/arch/arm64/kvm/va_layout.c
index 978301392d67..edb048654e00 100644
--- a/arch/arm64/kvm/va_layout.c
+++ b/arch/arm64/kvm/va_layout.c
@@ -156,6 +156,9 @@ void __init kvm_update_va_mask(struct alt_instr *alt,
 {
 	int i;
 
+	if (!is_hyp_mode_available())
+		return;
+
 	BUG_ON(nr_inst != 5);
 
 	for (i = 0; i < nr_inst; i++) {
@@ -191,6 +194,9 @@ void kvm_patch_vector_branch(struct alt_instr *alt,
 	u64 addr;
 	u32 insn;
 
+	if (!is_hyp_mode_available())
+		return;
+
 	BUG_ON(nr_inst != 4);
 
 	if (!cpus_have_const_cap(ARM64_SPECTRE_V3A) || WARN_ON_ONCE(has_vhe()))
@@ -244,6 +250,9 @@ static void generate_mov_q(u64 val, __le32 *origptr, __le32 *updptr, int nr_inst
 {
 	u32 insn, oinsn, rd;
 
+	if (!is_hyp_mode_available())
+		return;
+
 	BUG_ON(nr_inst != 4);
 
 	/* Compute target register */
-- 
2.29.2


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^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 2/3] arm64: Cope with CPUs stuck in VHE mode
  2021-03-30 17:39 ` [PATCH v2 2/3] arm64: Cope with CPUs stuck in VHE mode Marc Zyngier
@ 2021-04-07 21:16   ` Will Deacon
  0 siblings, 0 replies; 11+ messages in thread
From: Will Deacon @ 2021-04-07 21:16 UTC (permalink / raw)
  To: Marc Zyngier
  Cc: linux-arm-kernel, Hector Martin, Arnd Bergmann, Mark Rutland,
	Catalin Marinas, kernel-team

On Tue, Mar 30, 2021 at 06:39:46PM +0100, Marc Zyngier wrote:
> It seems that the CPUs part of the SoC known as Apple M1 have the
> terrible habit of being stuck with HCR_EL2.E2H==1, in violation
> of the architecture.
> 
> Try and work around this deplorable state of affairs by detecting
> the stuck bit early and short-circuit the nVHE dance. Additional
> filtering code ensures that attempts at switching to nVHE from
> the command-line are also ignored.
> 
> It is still unknown whether there are many more such nuggets
> to be found...
> 
> Reported-by: Hector Martin <marcan@marcan.st>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/kernel/head.S           | 39 +++++++++++++++++++++++++++---
>  arch/arm64/kernel/hyp-stub.S       |  8 +++---
>  arch/arm64/kernel/idreg-override.c | 13 +++++++++-
>  3 files changed, 52 insertions(+), 8 deletions(-)

Acked-by: Will Deacon <will@kernel.org>

Will

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^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 3/3] arm64: Allow nVHE impaired CPUs to boot without CONFIG_ARM64_VHE
  2021-03-30 17:39 ` [PATCH v2 3/3] arm64: Allow nVHE impaired CPUs to boot without CONFIG_ARM64_VHE Marc Zyngier
@ 2021-04-07 21:18   ` Will Deacon
  2021-04-08 10:31     ` Marc Zyngier
  0 siblings, 1 reply; 11+ messages in thread
From: Will Deacon @ 2021-04-07 21:18 UTC (permalink / raw)
  To: Marc Zyngier
  Cc: linux-arm-kernel, Hector Martin, Arnd Bergmann, Mark Rutland,
	Catalin Marinas, kernel-team

On Tue, Mar 30, 2021 at 06:39:47PM +0100, Marc Zyngier wrote:
> CPUs stuck in VHE mode need some additional care if the kernel
> is compiled without CONFIG_ARM64_VHE.
> 
> Treat this case as another version of a mismatched boot, and
> prevent KVM from being initialised. The machine will boot in
> some bizarre state, using TPIDR_EL1 instead of TPIDR_EL2, but
> otherwise be functional.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/include/asm/virt.h | 18 +++++++++++++-----
>  arch/arm64/kvm/va_layout.c    |  9 +++++++++
>  2 files changed, 22 insertions(+), 5 deletions(-)

Hmm, I think we definitely need _something_ here, but it's a bit annoying
to put ourselves into this weird state just for the sake of one stupid
machine.

What if we dropped CONFIG_ARM64_VHE and made the VHE code unconditional
instead? Is there a good reason to allow it to be disabled nowadays?

Will

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^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 3/3] arm64: Allow nVHE impaired CPUs to boot without CONFIG_ARM64_VHE
  2021-04-07 21:18   ` Will Deacon
@ 2021-04-08 10:31     ` Marc Zyngier
  2021-04-08 10:58       ` Will Deacon
  0 siblings, 1 reply; 11+ messages in thread
From: Marc Zyngier @ 2021-04-08 10:31 UTC (permalink / raw)
  To: Will Deacon
  Cc: linux-arm-kernel, Hector Martin, Arnd Bergmann, Mark Rutland,
	Catalin Marinas, kernel-team

On 2021-04-07 22:18, Will Deacon wrote:
> On Tue, Mar 30, 2021 at 06:39:47PM +0100, Marc Zyngier wrote:
>> CPUs stuck in VHE mode need some additional care if the kernel
>> is compiled without CONFIG_ARM64_VHE.
>> 
>> Treat this case as another version of a mismatched boot, and
>> prevent KVM from being initialised. The machine will boot in
>> some bizarre state, using TPIDR_EL1 instead of TPIDR_EL2, but
>> otherwise be functional.
>> 
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> ---
>>  arch/arm64/include/asm/virt.h | 18 +++++++++++++-----
>>  arch/arm64/kvm/va_layout.c    |  9 +++++++++
>>  2 files changed, 22 insertions(+), 5 deletions(-)
> 
> Hmm, I think we definitely need _something_ here, but it's a bit 
> annoying
> to put ourselves into this weird state just for the sake of one stupid
> machine.

Which is why I'm not keen at all on this patch, and I'm happy to see
the machine die a painful death. We really can't be blamed for 
terminally
buggy HW, which the M1 obviously is.

> What if we dropped CONFIG_ARM64_VHE and made the VHE code unconditional
> instead? Is there a good reason to allow it to be disabled nowadays?

What do we do for the other camp, aka people really wanting to run nVHE
without any command line parameter? I can't see why you'd want to do
that, but hey, that's only me.

I'd be quite happy to see CONFIG_ARM64_VHE go though. Let me know if you
want a patch doing that instead.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 3/3] arm64: Allow nVHE impaired CPUs to boot without CONFIG_ARM64_VHE
  2021-04-08 10:31     ` Marc Zyngier
@ 2021-04-08 10:58       ` Will Deacon
  2021-04-08 13:05         ` Marc Zyngier
  0 siblings, 1 reply; 11+ messages in thread
From: Will Deacon @ 2021-04-08 10:58 UTC (permalink / raw)
  To: Marc Zyngier
  Cc: linux-arm-kernel, Hector Martin, Arnd Bergmann, Mark Rutland,
	Catalin Marinas, kernel-team

On Thu, Apr 08, 2021 at 11:31:42AM +0100, Marc Zyngier wrote:
> On 2021-04-07 22:18, Will Deacon wrote:
> > On Tue, Mar 30, 2021 at 06:39:47PM +0100, Marc Zyngier wrote:
> > > CPUs stuck in VHE mode need some additional care if the kernel
> > > is compiled without CONFIG_ARM64_VHE.
> > > 
> > > Treat this case as another version of a mismatched boot, and
> > > prevent KVM from being initialised. The machine will boot in
> > > some bizarre state, using TPIDR_EL1 instead of TPIDR_EL2, but
> > > otherwise be functional.
> > > 
> > > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > > ---
> > >  arch/arm64/include/asm/virt.h | 18 +++++++++++++-----
> > >  arch/arm64/kvm/va_layout.c    |  9 +++++++++
> > >  2 files changed, 22 insertions(+), 5 deletions(-)
> > 
> > Hmm, I think we definitely need _something_ here, but it's a bit
> > annoying
> > to put ourselves into this weird state just for the sake of one stupid
> > machine.
> 
> Which is why I'm not keen at all on this patch, and I'm happy to see
> the machine die a painful death. We really can't be blamed for terminally
> buggy HW, which the M1 obviously is.

Perhaps, but it's not clear at all how the problem manifests and so we
_will_ be blamed when things go wonky, especially as the real culprits
all seem to be hiding...

> > What if we dropped CONFIG_ARM64_VHE and made the VHE code unconditional
> > instead? Is there a good reason to allow it to be disabled nowadays?
> 
> What do we do for the other camp, aka people really wanting to run nVHE
> without any command line parameter? I can't see why you'd want to do
> that, but hey, that's only me.

They can pass the command-line parameter, no? If we ever get CMDLINE_EXTEND
support back, they could even add it in there!

> I'd be quite happy to see CONFIG_ARM64_VHE go though. Let me know if you
> want a patch doing that instead.

Yes please.

Will

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^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 1/3] arm64: cpufeature: Allow early filtering of feature override
  2021-03-30 17:39 ` [PATCH v2 1/3] arm64: cpufeature: Allow early filtering of feature override Marc Zyngier
@ 2021-04-08 11:13   ` Hector Martin
  2021-04-08 13:11     ` Marc Zyngier
  0 siblings, 1 reply; 11+ messages in thread
From: Hector Martin @ 2021-04-08 11:13 UTC (permalink / raw)
  To: Marc Zyngier, linux-arm-kernel
  Cc: Arnd Bergmann, Mark Rutland, Will Deacon, Catalin Marinas, kernel-team

On 31/03/2021 02.39, Marc Zyngier wrote:
> + * @mask		Mask of the features that are overriden by @val

FYI, I checkpatched this by accident and it pointed out a typo 
('overridden').

It also complained about a tab thing in the next patch (the last hunk 
has a tab followed by 8 spaces), though that was just carried over from 
the line before the patch.

-- 
Hector Martin (marcan@marcan.st)
Public Key: https://mrcn.st/pub

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^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 3/3] arm64: Allow nVHE impaired CPUs to boot without CONFIG_ARM64_VHE
  2021-04-08 10:58       ` Will Deacon
@ 2021-04-08 13:05         ` Marc Zyngier
  0 siblings, 0 replies; 11+ messages in thread
From: Marc Zyngier @ 2021-04-08 13:05 UTC (permalink / raw)
  To: Will Deacon
  Cc: linux-arm-kernel, Hector Martin, Arnd Bergmann, Mark Rutland,
	Catalin Marinas, kernel-team

On Thu, 08 Apr 2021 11:58:23 +0100,
Will Deacon <will@kernel.org> wrote:
> 
> On Thu, Apr 08, 2021 at 11:31:42AM +0100, Marc Zyngier wrote:
> > On 2021-04-07 22:18, Will Deacon wrote:
> > > On Tue, Mar 30, 2021 at 06:39:47PM +0100, Marc Zyngier wrote:
> > > > CPUs stuck in VHE mode need some additional care if the kernel
> > > > is compiled without CONFIG_ARM64_VHE.
> > > > 
> > > > Treat this case as another version of a mismatched boot, and
> > > > prevent KVM from being initialised. The machine will boot in
> > > > some bizarre state, using TPIDR_EL1 instead of TPIDR_EL2, but
> > > > otherwise be functional.
> > > > 
> > > > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > > > ---
> > > >  arch/arm64/include/asm/virt.h | 18 +++++++++++++-----
> > > >  arch/arm64/kvm/va_layout.c    |  9 +++++++++
> > > >  2 files changed, 22 insertions(+), 5 deletions(-)
> > > 
> > > Hmm, I think we definitely need _something_ here, but it's a bit
> > > annoying
> > > to put ourselves into this weird state just for the sake of one stupid
> > > machine.
> > 
> > Which is why I'm not keen at all on this patch, and I'm happy to see
> > the machine die a painful death. We really can't be blamed for terminally
> > buggy HW, which the M1 obviously is.
> 
> Perhaps, but it's not clear at all how the problem manifests and so we
> _will_ be blamed when things go wonky, especially as the real culprits
> all seem to be hiding...
> 
> > > What if we dropped CONFIG_ARM64_VHE and made the VHE code unconditional
> > > instead? Is there a good reason to allow it to be disabled nowadays?
> > 
> > What do we do for the other camp, aka people really wanting to run nVHE
> > without any command line parameter? I can't see why you'd want to do
> > that, but hey, that's only me.
> 
> They can pass the command-line parameter, no? If we ever get CMDLINE_EXTEND
> support back, they could even add it in there!

My point was that they could do it *without* the parameter. No skin
off my nose anyway.

> 
> > I'd be quite happy to see CONFIG_ARM64_VHE go though. Let me know if you
> > want a patch doing that instead.
> 
> Yes please.

Right, let me repost the series then.

	M.

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

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^ permalink raw reply	[flat|nested] 11+ messages in thread

* Re: [PATCH v2 1/3] arm64: cpufeature: Allow early filtering of feature override
  2021-04-08 11:13   ` Hector Martin
@ 2021-04-08 13:11     ` Marc Zyngier
  0 siblings, 0 replies; 11+ messages in thread
From: Marc Zyngier @ 2021-04-08 13:11 UTC (permalink / raw)
  To: Hector Martin
  Cc: linux-arm-kernel, Arnd Bergmann, Mark Rutland, Will Deacon,
	Catalin Marinas, kernel-team

On Thu, 08 Apr 2021 12:13:44 +0100,
Hector Martin <marcan@marcan.st> wrote:
> 
> On 31/03/2021 02.39, Marc Zyngier wrote:
> > + * @mask		Mask of the features that are overriden by @val
> 
> FYI, I checkpatched this by accident and it pointed out a typo
> ('overridden').

My prefered fix would be not to run checkpatch, but since you found
it... ;-)

> It also complained about a tab thing in the next patch (the last hunk
> has a tab followed by 8 spaces), though that was just carried over
> from the line before the patch.

Fixed both in v3 which I just posted.

Thanks,

	M.

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

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^ permalink raw reply	[flat|nested] 11+ messages in thread

end of thread, other threads:[~2021-04-08 13:13 UTC | newest]

Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-03-30 17:39 [PATCH v2 0/3] arm64: Dealing with VHE-only CPUs Marc Zyngier
2021-03-30 17:39 ` [PATCH v2 1/3] arm64: cpufeature: Allow early filtering of feature override Marc Zyngier
2021-04-08 11:13   ` Hector Martin
2021-04-08 13:11     ` Marc Zyngier
2021-03-30 17:39 ` [PATCH v2 2/3] arm64: Cope with CPUs stuck in VHE mode Marc Zyngier
2021-04-07 21:16   ` Will Deacon
2021-03-30 17:39 ` [PATCH v2 3/3] arm64: Allow nVHE impaired CPUs to boot without CONFIG_ARM64_VHE Marc Zyngier
2021-04-07 21:18   ` Will Deacon
2021-04-08 10:31     ` Marc Zyngier
2021-04-08 10:58       ` Will Deacon
2021-04-08 13:05         ` Marc Zyngier

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