[3/3] KVM: arm/arm64: correct AArch32 SPSR on exception entry

Message ID 20191220150549.31948-4-mark.rutland@arm.com
State Accepted
Commit 1cfbb484de158e378e8971ac40f3082e53ecca55
Headers show
Series
  • [1/3] KVM: arm64: correct PSTATE on exception entry
Related show

Commit Message

Mark Rutland Dec. 20, 2019, 3:05 p.m.
Confusingly, there are three SPSR layouts that a kernel may need to deal
with:

(1) An AArch64 SPSR_ELx view of an AArch64 pstate
(2) An AArch64 SPSR_ELx view of an AArch32 pstate
(3) An AArch32 SPSR_* view of an AArch32 pstate

When the KVM AArch32 support code deals with SPSR_{EL2,HYP}, it's either
dealing with #2 or #3 consistently. On arm64 the PSR_AA32_* definitions
match the AArch64 SPSR_ELx view, and on arm the PSR_AA32_* definitions
match the AArch32 SPSR_* view.

However, when we inject an exception into an AArch32 guest, we have to
synthesize the AArch32 SPSR_* that the guest will see. Thus, an AArch64
host needs to synthesize layout #3 from layout #2.

This patch adds a new host_spsr_to_spsr32() helper for this, and makes
use of it in the KVM AArch32 support code. For arm64 we need to shuffle
the DIT bit around, and remove the SS bit, while for arm we can use the
value as-is.

I've open-coded the bit manipulation for now to avoid having to rework
the existing PSR_* definitions into PSR64_AA32_* and PSR32_AA32_*
definitions. I hope to perform a more thorough refactoring in future so
that we can handle pstate view manipulation more consistently across the
kernel tree.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>

Cc: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: Drew Jones <drjones@redhat.com>
Cc: James Morse <james.morse@arm.com>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: stable@vger.kernel.org
---
 arch/arm/include/asm/kvm_emulate.h   |  5 +++++
 arch/arm64/include/asm/kvm_emulate.h | 32 ++++++++++++++++++++++++++++++++
 virt/kvm/arm/aarch32.c               |  6 +++---
 3 files changed, 40 insertions(+), 3 deletions(-)

-- 
2.11.0

Comments

Marc Zyngier Dec. 20, 2019, 3:36 p.m. | #1
Hi Mark,

On 2019-12-20 15:05, Mark Rutland wrote:
> Confusingly, there are three SPSR layouts that a kernel may need to 

> deal

> with:

>

> (1) An AArch64 SPSR_ELx view of an AArch64 pstate

> (2) An AArch64 SPSR_ELx view of an AArch32 pstate

> (3) An AArch32 SPSR_* view of an AArch32 pstate

>

> When the KVM AArch32 support code deals with SPSR_{EL2,HYP}, it's 

> either

> dealing with #2 or #3 consistently. On arm64 the PSR_AA32_* 

> definitions

> match the AArch64 SPSR_ELx view, and on arm the PSR_AA32_* 

> definitions

> match the AArch32 SPSR_* view.

>

> However, when we inject an exception into an AArch32 guest, we have 

> to

> synthesize the AArch32 SPSR_* that the guest will see. Thus, an 

> AArch64

> host needs to synthesize layout #3 from layout #2.

>

> This patch adds a new host_spsr_to_spsr32() helper for this, and 

> makes

> use of it in the KVM AArch32 support code. For arm64 we need to 

> shuffle

> the DIT bit around, and remove the SS bit, while for arm we can use 

> the

> value as-is.

>

> I've open-coded the bit manipulation for now to avoid having to 

> rework

> the existing PSR_* definitions into PSR64_AA32_* and PSR32_AA32_*

> definitions. I hope to perform a more thorough refactoring in future 

> so

> that we can handle pstate view manipulation more consistently across 

> the

> kernel tree.

>

> Signed-off-by: Mark Rutland <mark.rutland@arm.com>

> Cc: Alexandru Elisei <alexandru.elisei@arm.com>

> Cc: Drew Jones <drjones@redhat.com>

> Cc: James Morse <james.morse@arm.com>

> Cc: Julien Thierry <julien.thierry.kdev@gmail.com>

> Cc: Marc Zyngier <maz@kernel.org>

> Cc: Peter Maydell <peter.maydell@linaro.org>

> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>

> Cc: Will Deacon <will@kernel.org>

> Cc: stable@vger.kernel.org

> ---

>  arch/arm/include/asm/kvm_emulate.h   |  5 +++++

>  arch/arm64/include/asm/kvm_emulate.h | 32 

> ++++++++++++++++++++++++++++++++

>  virt/kvm/arm/aarch32.c               |  6 +++---

>  3 files changed, 40 insertions(+), 3 deletions(-)

>

> diff --git a/arch/arm/include/asm/kvm_emulate.h

> b/arch/arm/include/asm/kvm_emulate.h

> index dee2567661ed..b811576bc456 100644

> --- a/arch/arm/include/asm/kvm_emulate.h

> +++ b/arch/arm/include/asm/kvm_emulate.h

> @@ -53,6 +53,11 @@ static inline void vcpu_write_spsr(struct kvm_vcpu

> *vcpu, unsigned long v)

>  	*__vcpu_spsr(vcpu) = v;

>  }

>

> +static inline unsigned long host_spsr_to_spsr32(unsigned long spsr)

> +{

> +	return spsr;

> +}

> +

>  static inline unsigned long vcpu_get_reg(struct kvm_vcpu *vcpu,

>  					 u8 reg_num)

>  {

> diff --git a/arch/arm64/include/asm/kvm_emulate.h

> b/arch/arm64/include/asm/kvm_emulate.h

> index d69c1efc63e7..98672938f9f9 100644

> --- a/arch/arm64/include/asm/kvm_emulate.h

> +++ b/arch/arm64/include/asm/kvm_emulate.h

> @@ -204,6 +204,38 @@ static inline void vcpu_write_spsr(struct

> kvm_vcpu *vcpu, unsigned long v)

>  		vcpu_gp_regs(vcpu)->spsr[KVM_SPSR_EL1] = v;

>  }

>

> +/*

> + * The layout of SPSR for an AArch32 state is different when

> observed from an

> + * AArch64 SPSR_ELx or an AArch32 SPSR_*. This function generates

> the AArch32

> + * view given an AArch64 view.

> + *

> + * In ARM DDI 0487E.a see:

> + *

> + * - The AArch64 view (SPSR_EL2) in section C5.2.18, page C5-426

> + * - The AArch32 view (SPSR_abt) in section G8.2.126, page G8-6256

> + * - The AArch32 view (SPSR_und) in section G8.2.132, page G8-6280

> + *

> + * Which show the following differences:

> + *

> + * | Bit | AA64 | AA32 | Notes                       |

> + * +-----+------+------+-----------------------------|

> + * | 24  | DIT  | J    | J is RES0 in ARMv8          |

> + * | 21  | SS   | DIT  | SS doesn't exist in AArch32 |

> + *

> + * ... and all other bits are (currently) common.

> + */

> +static inline unsigned long host_spsr_to_spsr32(unsigned long spsr)

> +{

> +	const unsigned long overlap = BIT(24) | BIT(21);

> +	unsigned long dit = !!(spsr & PSR_AA32_DIT_BIT);

> +

> +	spsr &= overlap;


Are you sure this is what you want to do? This doesn't leave
that many bits set in SPSR... :-/

> +

> +	spsr |= dit << 21;

> +

> +	return spsr;

> +}

> +

>  static inline bool vcpu_mode_priv(const struct kvm_vcpu *vcpu)

>  {

>  	u32 mode;

> diff --git a/virt/kvm/arm/aarch32.c b/virt/kvm/arm/aarch32.c

> index 17bcde5c2451..115210e64682 100644

> --- a/virt/kvm/arm/aarch32.c

> +++ b/virt/kvm/arm/aarch32.c

> @@ -128,15 +128,15 @@ static unsigned long get_except32_cpsr(struct

> kvm_vcpu *vcpu, u32 mode)

>

>  static void prepare_fault32(struct kvm_vcpu *vcpu, u32 mode, u32

> vect_offset)

>  {

> -	unsigned long new_spsr_value = *vcpu_cpsr(vcpu);

> -	bool is_thumb = (new_spsr_value & PSR_AA32_T_BIT);

> +	unsigned long spsr = *vcpu_cpsr(vcpu);

> +	bool is_thumb = (spsr & PSR_AA32_T_BIT);

>  	u32 return_offset = return_offsets[vect_offset >> 2][is_thumb];

>  	u32 sctlr = vcpu_cp15(vcpu, c1_SCTLR);

>

>  	*vcpu_cpsr(vcpu) = get_except32_cpsr(vcpu, mode);

>

>  	/* Note: These now point to the banked copies */

> -	vcpu_write_spsr(vcpu, new_spsr_value);

> +	vcpu_write_spsr(vcpu, host_spsr_to_spsr32(spsr));

>  	*vcpu_reg32(vcpu, 14) = *vcpu_pc(vcpu) + return_offset;

>

>  	/* Branch to exception vector */


Apart from what I believe is a missing ~ above, this looks good.

         M.
-- 
Jazz is not dead. It just smells funny...
Mark Rutland Dec. 20, 2019, 3:44 p.m. | #2
On Fri, Dec 20, 2019 at 03:36:47PM +0000, Marc Zyngier wrote:
> On 2019-12-20 15:05, Mark Rutland wrote:

> > +static inline unsigned long host_spsr_to_spsr32(unsigned long spsr)

> > +{

> > +	const unsigned long overlap = BIT(24) | BIT(21);

> > +	unsigned long dit = !!(spsr & PSR_AA32_DIT_BIT);

> > +

> > +	spsr &= overlap;

> 

> Are you sure this is what you want to do? This doesn't leave

> that many bits set in SPSR... :-/


Oh, whoops. :(

> Apart from what I believe is a missing ~ above, this looks good.


I've added the missing '~' and pushed out the updated branch.

Thanks,
Mark.
Alexandru Elisei Dec. 27, 2019, 3:56 p.m. | #3
Hi,

On 12/20/19 3:05 PM, Mark Rutland wrote:
> Confusingly, there are three SPSR layouts that a kernel may need to deal

> with:

>

> (1) An AArch64 SPSR_ELx view of an AArch64 pstate

> (2) An AArch64 SPSR_ELx view of an AArch32 pstate

> (3) An AArch32 SPSR_* view of an AArch32 pstate

>

> When the KVM AArch32 support code deals with SPSR_{EL2,HYP}, it's either

> dealing with #2 or #3 consistently. On arm64 the PSR_AA32_* definitions

> match the AArch64 SPSR_ELx view, and on arm the PSR_AA32_* definitions

> match the AArch32 SPSR_* view.

>

> However, when we inject an exception into an AArch32 guest, we have to

> synthesize the AArch32 SPSR_* that the guest will see. Thus, an AArch64

> host needs to synthesize layout #3 from layout #2.

>

> This patch adds a new host_spsr_to_spsr32() helper for this, and makes

> use of it in the KVM AArch32 support code. For arm64 we need to shuffle

> the DIT bit around, and remove the SS bit, while for arm we can use the

> value as-is.

>

> I've open-coded the bit manipulation for now to avoid having to rework

> the existing PSR_* definitions into PSR64_AA32_* and PSR32_AA32_*

> definitions. I hope to perform a more thorough refactoring in future so

> that we can handle pstate view manipulation more consistently across the

> kernel tree.

>

> Signed-off-by: Mark Rutland <mark.rutland@arm.com>

> Cc: Alexandru Elisei <alexandru.elisei@arm.com>

> Cc: Drew Jones <drjones@redhat.com>

> Cc: James Morse <james.morse@arm.com>

> Cc: Julien Thierry <julien.thierry.kdev@gmail.com>

> Cc: Marc Zyngier <maz@kernel.org>

> Cc: Peter Maydell <peter.maydell@linaro.org>

> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>

> Cc: Will Deacon <will@kernel.org>

> Cc: stable@vger.kernel.org

> ---

>  arch/arm/include/asm/kvm_emulate.h   |  5 +++++

>  arch/arm64/include/asm/kvm_emulate.h | 32 ++++++++++++++++++++++++++++++++

>  virt/kvm/arm/aarch32.c               |  6 +++---

>  3 files changed, 40 insertions(+), 3 deletions(-)

>

> diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h

> index dee2567661ed..b811576bc456 100644

> --- a/arch/arm/include/asm/kvm_emulate.h

> +++ b/arch/arm/include/asm/kvm_emulate.h

> @@ -53,6 +53,11 @@ static inline void vcpu_write_spsr(struct kvm_vcpu *vcpu, unsigned long v)

>  	*__vcpu_spsr(vcpu) = v;

>  }

>  

> +static inline unsigned long host_spsr_to_spsr32(unsigned long spsr)

> +{

> +	return spsr;

> +}

> +

>  static inline unsigned long vcpu_get_reg(struct kvm_vcpu *vcpu,

>  					 u8 reg_num)

>  {

> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h

> index d69c1efc63e7..98672938f9f9 100644

> --- a/arch/arm64/include/asm/kvm_emulate.h

> +++ b/arch/arm64/include/asm/kvm_emulate.h

> @@ -204,6 +204,38 @@ static inline void vcpu_write_spsr(struct kvm_vcpu *vcpu, unsigned long v)

>  		vcpu_gp_regs(vcpu)->spsr[KVM_SPSR_EL1] = v;

>  }

>  

> +/*

> + * The layout of SPSR for an AArch32 state is different when observed from an

> + * AArch64 SPSR_ELx or an AArch32 SPSR_*. This function generates the AArch32

> + * view given an AArch64 view.

> + *

> + * In ARM DDI 0487E.a see:

> + *

> + * - The AArch64 view (SPSR_EL2) in section C5.2.18, page C5-426

> + * - The AArch32 view (SPSR_abt) in section G8.2.126, page G8-6256

> + * - The AArch32 view (SPSR_und) in section G8.2.132, page G8-6280

> + *

> + * Which show the following differences:

> + *

> + * | Bit | AA64 | AA32 | Notes                       |

> + * +-----+------+------+-----------------------------|

> + * | 24  | DIT  | J    | J is RES0 in ARMv8          |

> + * | 21  | SS   | DIT  | SS doesn't exist in AArch32 |

> + *

> + * ... and all other bits are (currently) common.

> + */

> +static inline unsigned long host_spsr_to_spsr32(unsigned long spsr)

> +{

> +	const unsigned long overlap = BIT(24) | BIT(21);

> +	unsigned long dit = !!(spsr & PSR_AA32_DIT_BIT);

> +

> +	spsr &= overlap;

> +

> +	spsr |= dit << 21;

> +

> +	return spsr;

> +}

> +

>  static inline bool vcpu_mode_priv(const struct kvm_vcpu *vcpu)

>  {

>  	u32 mode;

> diff --git a/virt/kvm/arm/aarch32.c b/virt/kvm/arm/aarch32.c

> index 17bcde5c2451..115210e64682 100644

> --- a/virt/kvm/arm/aarch32.c

> +++ b/virt/kvm/arm/aarch32.c

> @@ -128,15 +128,15 @@ static unsigned long get_except32_cpsr(struct kvm_vcpu *vcpu, u32 mode)

>  

>  static void prepare_fault32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset)

>  {

> -	unsigned long new_spsr_value = *vcpu_cpsr(vcpu);

> -	bool is_thumb = (new_spsr_value & PSR_AA32_T_BIT);

> +	unsigned long spsr = *vcpu_cpsr(vcpu);

> +	bool is_thumb = (spsr & PSR_AA32_T_BIT);

>  	u32 return_offset = return_offsets[vect_offset >> 2][is_thumb];

>  	u32 sctlr = vcpu_cp15(vcpu, c1_SCTLR);

>  

>  	*vcpu_cpsr(vcpu) = get_except32_cpsr(vcpu, mode);

>  

>  	/* Note: These now point to the banked copies */

> -	vcpu_write_spsr(vcpu, new_spsr_value);

> +	vcpu_write_spsr(vcpu, host_spsr_to_spsr32(spsr));

>  	*vcpu_reg32(vcpu, 14) = *vcpu_pc(vcpu) + return_offset;

>  

>  	/* Branch to exception vector */


With Marc's comment fixed:

Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>


Thanks,
Alex

Patch

diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h
index dee2567661ed..b811576bc456 100644
--- a/arch/arm/include/asm/kvm_emulate.h
+++ b/arch/arm/include/asm/kvm_emulate.h
@@ -53,6 +53,11 @@  static inline void vcpu_write_spsr(struct kvm_vcpu *vcpu, unsigned long v)
 	*__vcpu_spsr(vcpu) = v;
 }
 
+static inline unsigned long host_spsr_to_spsr32(unsigned long spsr)
+{
+	return spsr;
+}
+
 static inline unsigned long vcpu_get_reg(struct kvm_vcpu *vcpu,
 					 u8 reg_num)
 {
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index d69c1efc63e7..98672938f9f9 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -204,6 +204,38 @@  static inline void vcpu_write_spsr(struct kvm_vcpu *vcpu, unsigned long v)
 		vcpu_gp_regs(vcpu)->spsr[KVM_SPSR_EL1] = v;
 }
 
+/*
+ * The layout of SPSR for an AArch32 state is different when observed from an
+ * AArch64 SPSR_ELx or an AArch32 SPSR_*. This function generates the AArch32
+ * view given an AArch64 view.
+ *
+ * In ARM DDI 0487E.a see:
+ *
+ * - The AArch64 view (SPSR_EL2) in section C5.2.18, page C5-426
+ * - The AArch32 view (SPSR_abt) in section G8.2.126, page G8-6256
+ * - The AArch32 view (SPSR_und) in section G8.2.132, page G8-6280
+ *
+ * Which show the following differences:
+ *
+ * | Bit | AA64 | AA32 | Notes                       |
+ * +-----+------+------+-----------------------------|
+ * | 24  | DIT  | J    | J is RES0 in ARMv8          |
+ * | 21  | SS   | DIT  | SS doesn't exist in AArch32 |
+ *
+ * ... and all other bits are (currently) common.
+ */
+static inline unsigned long host_spsr_to_spsr32(unsigned long spsr)
+{
+	const unsigned long overlap = BIT(24) | BIT(21);
+	unsigned long dit = !!(spsr & PSR_AA32_DIT_BIT);
+
+	spsr &= overlap;
+
+	spsr |= dit << 21;
+
+	return spsr;
+}
+
 static inline bool vcpu_mode_priv(const struct kvm_vcpu *vcpu)
 {
 	u32 mode;
diff --git a/virt/kvm/arm/aarch32.c b/virt/kvm/arm/aarch32.c
index 17bcde5c2451..115210e64682 100644
--- a/virt/kvm/arm/aarch32.c
+++ b/virt/kvm/arm/aarch32.c
@@ -128,15 +128,15 @@  static unsigned long get_except32_cpsr(struct kvm_vcpu *vcpu, u32 mode)
 
 static void prepare_fault32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset)
 {
-	unsigned long new_spsr_value = *vcpu_cpsr(vcpu);
-	bool is_thumb = (new_spsr_value & PSR_AA32_T_BIT);
+	unsigned long spsr = *vcpu_cpsr(vcpu);
+	bool is_thumb = (spsr & PSR_AA32_T_BIT);
 	u32 return_offset = return_offsets[vect_offset >> 2][is_thumb];
 	u32 sctlr = vcpu_cp15(vcpu, c1_SCTLR);
 
 	*vcpu_cpsr(vcpu) = get_except32_cpsr(vcpu, mode);
 
 	/* Note: These now point to the banked copies */
-	vcpu_write_spsr(vcpu, new_spsr_value);
+	vcpu_write_spsr(vcpu, host_spsr_to_spsr32(spsr));
 	*vcpu_reg32(vcpu, 14) = *vcpu_pc(vcpu) + return_offset;
 
 	/* Branch to exception vector */