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[PATCH v2 4/6] x86/fpu/xstate: Introduce fpu_guest_cfg for guest FPU configuration

Chao Gao posted 6 patches 1 year, 2 months ago
There is a newer version of this series
[PATCH v2 4/6] x86/fpu/xstate: Introduce fpu_guest_cfg for guest FPU configuration
Posted by Chao Gao 1 year, 2 months ago 
From: Yang Weijiang <weijiang.yang@intel.com>

Define new fpu_guest_cfg to hold all guest FPU settings so that it can
differ from generic kernel FPU settings, e.g., enabling CET supervisor
xstate by default for guest fpstate while it's remained disabled in
kernel FPU config.

The kernel dynamic xfeatures are specifically used by guest fpstate now,
add the mask for guest fpstate so that guest_perm.__state_perm ==
(fpu_kernel_cfg.default_xfeature | XFEATURE_MASK_KERNEL_DYNAMIC). And
if guest fpstate is re-allocated to hold user dynamic xfeatures, the
resulting permissions are consumed before calculate new guest fpstate.

With new guest FPU config added, there're 3 categories of FPU configs in
kernel, the usages and key fields are recapped as below.

kernel FPU config:
  @fpu_kernel_cfg.max_features
  - all known and CPU supported user and supervisor features except
    independent kernel features

  @fpu_kernel_cfg.default_features
  - all known and CPU supported user and supervisor features except
    dynamic kernel features, independent kernel features and dynamic
    userspace features.

  @fpu_kernel_cfg.max_size
  - size of compacted buffer with 'fpu_kernel_cfg.max_features'

  @fpu_kernel_cfg.default_size
  - size of compacted buffer with 'fpu_kernel_cfg.default_features'

user FPU config:
  @fpu_user_cfg.max_features
  - all known and CPU supported user features

  @fpu_user_cfg.default_features
  - all known and CPU supported user features except dynamic userspace
    features.

  @fpu_user_cfg.max_size
  - size of non-compacted buffer with 'fpu_user_cfg.max_features'

  @fpu_user_cfg.default_size
  - size of non-compacted buffer with 'fpu_user_cfg.default_features'

guest FPU config:
  @fpu_guest_cfg.max_features
  - all known and CPU supported user and supervisor features except
    independent kernel features.

  @fpu_guest_cfg.default_features
  - all known and CPU supported user and supervisor features except
    independent kernel features and dynamic userspace features.

  @fpu_guest_cfg.max_size
  - size of compacted buffer with 'fpu_guest_cfg.max_features'

  @fpu_guest_cfg.default_size
  - size of compacted buffer with 'fpu_guest_cfg.default_features'

Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 arch/x86/include/asm/fpu/types.h |  2 +-
 arch/x86/kernel/fpu/core.c       | 14 +++++++++++---
 arch/x86/kernel/fpu/xstate.c     | 10 ++++++++++
 3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index b49e65120d34..da6583a1c0a2 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -611,6 +611,6 @@ struct fpu_state_config {
 };
 
 /* FPU state configuration information */
-extern struct fpu_state_config fpu_kernel_cfg, fpu_user_cfg;
+extern struct fpu_state_config fpu_kernel_cfg, fpu_user_cfg, fpu_guest_cfg;
 
 #endif /* _ASM_X86_FPU_TYPES_H */
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 1209c7aebb21..9e2e5c46cf28 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -33,9 +33,10 @@ DEFINE_STATIC_KEY_FALSE(__fpu_state_size_dynamic);
 DEFINE_PER_CPU(u64, xfd_state);
 #endif
 
-/* The FPU state configuration data for kernel and user space */
+/* The FPU state configuration data for kernel, user space and guest. */
 struct fpu_state_config	fpu_kernel_cfg __ro_after_init;
 struct fpu_state_config fpu_user_cfg __ro_after_init;
+struct fpu_state_config fpu_guest_cfg __ro_after_init;
 
 /*
  * Represents the initial FPU state. It's mostly (but not completely) zeroes,
@@ -536,8 +537,15 @@ void fpstate_reset(struct fpu *fpu)
 	fpu->perm.__state_perm		= fpu_kernel_cfg.default_features;
 	fpu->perm.__state_size		= fpu_kernel_cfg.default_size;
 	fpu->perm.__user_state_size	= fpu_user_cfg.default_size;
-	/* Same defaults for guests */
-	fpu->guest_perm = fpu->perm;
+
+	/* Guest permission settings */
+	fpu->guest_perm.__state_perm	= fpu_guest_cfg.default_features;
+	fpu->guest_perm.__state_size	= fpu_guest_cfg.default_size;
+	/*
+	 * Set guest's __user_state_size to fpu_user_cfg.default_size so that
+	 * existing uAPIs can still work.
+	 */
+	fpu->guest_perm.__user_state_size = fpu_user_cfg.default_size;
 }
 
 static inline void fpu_inherit_perms(struct fpu *dst_fpu)
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index c38e477e3e45..17c3255dfa41 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -686,6 +686,7 @@ static int __init init_xstate_size(void)
 {
 	/* Recompute the context size for enabled features: */
 	unsigned int user_size, kernel_size, kernel_default_size;
+	unsigned int guest_default_size;
 	bool compacted = cpu_feature_enabled(X86_FEATURE_XCOMPACTED);
 
 	/* Uncompacted user space size */
@@ -707,13 +708,18 @@ static int __init init_xstate_size(void)
 	kernel_default_size =
 		xstate_calculate_size(fpu_kernel_cfg.default_features, compacted);
 
+	guest_default_size =
+		xstate_calculate_size(fpu_guest_cfg.default_features, compacted);
+
 	if (!paranoid_xstate_size_valid(kernel_size))
 		return -EINVAL;
 
 	fpu_kernel_cfg.max_size = kernel_size;
 	fpu_user_cfg.max_size = user_size;
+	fpu_guest_cfg.max_size = kernel_size;
 
 	fpu_kernel_cfg.default_size = kernel_default_size;
+	fpu_guest_cfg.default_size = guest_default_size;
 	fpu_user_cfg.default_size =
 		xstate_calculate_size(fpu_user_cfg.default_features, false);
 
@@ -829,6 +835,10 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
 	fpu_user_cfg.default_features = fpu_user_cfg.max_features;
 	fpu_user_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
 
+	fpu_guest_cfg.max_features = fpu_kernel_cfg.max_features;
+	fpu_guest_cfg.default_features = fpu_guest_cfg.max_features;
+	fpu_guest_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
+
 	/* Store it for paranoia check at the end */
 	xfeatures = fpu_kernel_cfg.max_features;
 
-- 
2.46.1
Re: [PATCH v2 4/6] x86/fpu/xstate: Introduce fpu_guest_cfg for guest FPU configuration
Posted by Dave Hansen 11 months, 1 week ago 
On 11/26/24 02:17, Chao Gao wrote:
> From: Yang Weijiang <weijiang.yang@intel.com>
> 
> Define new fpu_guest_cfg to hold all guest FPU settings so that it can
> differ from generic kernel FPU settings, e.g., enabling CET supervisor
> xstate by default for guest fpstate while it's remained disabled in
> kernel FPU config.
> 
> The kernel dynamic xfeatures are specifically used by guest fpstate now,
> add the mask for guest fpstate so that guest_perm.__state_perm ==
> (fpu_kernel_cfg.default_xfeature | XFEATURE_MASK_KERNEL_DYNAMIC). And
> if guest fpstate is re-allocated to hold user dynamic xfeatures, the
> resulting permissions are consumed before calculate new guest fpstate.

This kinda restates what the code does, but I don't think it matches the
code.

> With new guest FPU config added, there're 3 categories of FPU configs in
> kernel, the usages and key fields are recapped as below.

This changelog is pretty rough. It's got a lot of words but not much
substance.


> kernel FPU config:
>   @fpu_kernel_cfg.max_features
>   - all known and CPU supported user and supervisor features except
>     independent kernel features
> 
>   @fpu_kernel_cfg.default_features
>   - all known and CPU supported user and supervisor features except
>     dynamic kernel features, independent kernel features and dynamic
>     userspace features.
> 
>   @fpu_kernel_cfg.max_size
>   - size of compacted buffer with 'fpu_kernel_cfg.max_features'
> 
>   @fpu_kernel_cfg.default_size
>   - size of compacted buffer with 'fpu_kernel_cfg.default_features'
> 
> user FPU config:
>   @fpu_user_cfg.max_features
>   - all known and CPU supported user features
> 
>   @fpu_user_cfg.default_features
>   - all known and CPU supported user features except dynamic userspace
>     features.
> 
>   @fpu_user_cfg.max_size
>   - size of non-compacted buffer with 'fpu_user_cfg.max_features'
> 
>   @fpu_user_cfg.default_size
>   - size of non-compacted buffer with 'fpu_user_cfg.default_features'
> 
> guest FPU config:
>   @fpu_guest_cfg.max_features
>   - all known and CPU supported user and supervisor features except
>     independent kernel features.
> 
>   @fpu_guest_cfg.default_features
>   - all known and CPU supported user and supervisor features except
>     independent kernel features and dynamic userspace features.
> 
>   @fpu_guest_cfg.max_size
>   - size of compacted buffer with 'fpu_guest_cfg.max_features'
> 
>   @fpu_guest_cfg.default_size
>   - size of compacted buffer with 'fpu_guest_cfg.default_features'

This looks like kerneldoc, not changelog. Are you sure you want it _here_?


> diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
> index b49e65120d34..da6583a1c0a2 100644
> --- a/arch/x86/include/asm/fpu/types.h
> +++ b/arch/x86/include/asm/fpu/types.h
> @@ -611,6 +611,6 @@ struct fpu_state_config {
>  };
>  
>  /* FPU state configuration information */
> -extern struct fpu_state_config fpu_kernel_cfg, fpu_user_cfg;
> +extern struct fpu_state_config fpu_kernel_cfg, fpu_user_cfg, fpu_guest_cfg;
>  
>  #endif /* _ASM_X86_FPU_TYPES_H */
> diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> index 1209c7aebb21..9e2e5c46cf28 100644
> --- a/arch/x86/kernel/fpu/core.c
> +++ b/arch/x86/kernel/fpu/core.c
> @@ -33,9 +33,10 @@ DEFINE_STATIC_KEY_FALSE(__fpu_state_size_dynamic);
>  DEFINE_PER_CPU(u64, xfd_state);
>  #endif
>  
> -/* The FPU state configuration data for kernel and user space */
> +/* The FPU state configuration data for kernel, user space and guest. */
>  struct fpu_state_config	fpu_kernel_cfg __ro_after_init;
>  struct fpu_state_config fpu_user_cfg __ro_after_init;
> +struct fpu_state_config fpu_guest_cfg __ro_after_init;
>  
>  /*
>   * Represents the initial FPU state. It's mostly (but not completely) zeroes,
> @@ -536,8 +537,15 @@ void fpstate_reset(struct fpu *fpu)
>  	fpu->perm.__state_perm		= fpu_kernel_cfg.default_features;
>  	fpu->perm.__state_size		= fpu_kernel_cfg.default_size;
>  	fpu->perm.__user_state_size	= fpu_user_cfg.default_size;
> -	/* Same defaults for guests */
> -	fpu->guest_perm = fpu->perm;
> +
> +	/* Guest permission settings */
> +	fpu->guest_perm.__state_perm	= fpu_guest_cfg.default_features;
> +	fpu->guest_perm.__state_size	= fpu_guest_cfg.default_size;
> +	/*
> +	 * Set guest's __user_state_size to fpu_user_cfg.default_size so that
> +	 * existing uAPIs can still work.
> +	 */
> +	fpu->guest_perm.__user_state_size = fpu_user_cfg.default_size;
>  }
>  
>  static inline void fpu_inherit_perms(struct fpu *dst_fpu)
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index c38e477e3e45..17c3255dfa41 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -686,6 +686,7 @@ static int __init init_xstate_size(void)
>  {
>  	/* Recompute the context size for enabled features: */
>  	unsigned int user_size, kernel_size, kernel_default_size;
> +	unsigned int guest_default_size;
>  	bool compacted = cpu_feature_enabled(X86_FEATURE_XCOMPACTED);
>  
>  	/* Uncompacted user space size */
> @@ -707,13 +708,18 @@ static int __init init_xstate_size(void)
>  	kernel_default_size =
>  		xstate_calculate_size(fpu_kernel_cfg.default_features, compacted);
>  
> +	guest_default_size =
> +		xstate_calculate_size(fpu_guest_cfg.default_features, compacted);
> +
>  	if (!paranoid_xstate_size_valid(kernel_size))
>  		return -EINVAL;
>  
>  	fpu_kernel_cfg.max_size = kernel_size;
>  	fpu_user_cfg.max_size = user_size;
> +	fpu_guest_cfg.max_size = kernel_size;
>  
>  	fpu_kernel_cfg.default_size = kernel_default_size;
> +	fpu_guest_cfg.default_size = guest_default_size;
>  	fpu_user_cfg.default_size =
>  		xstate_calculate_size(fpu_user_cfg.default_features, false);
>  
> @@ -829,6 +835,10 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
>  	fpu_user_cfg.default_features = fpu_user_cfg.max_features;
>  	fpu_user_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
>  
> +	fpu_guest_cfg.max_features = fpu_kernel_cfg.max_features;
> +	fpu_guest_cfg.default_features = fpu_guest_cfg.max_features;
> +	fpu_guest_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;

I thought this was saying above that it was _setting_ dynamic features.

Why _not_ set them by default?
Re: [PATCH v2 4/6] x86/fpu/xstate: Introduce fpu_guest_cfg for guest FPU configuration
Posted by Chao Gao 11 months, 1 week ago 
On Tue, Mar 04, 2025 at 02:50:48PM -0800, Dave Hansen wrote:
>On 11/26/24 02:17, Chao Gao wrote:
>> From: Yang Weijiang <weijiang.yang@intel.com>
>> 
>> Define new fpu_guest_cfg to hold all guest FPU settings so that it can
>> differ from generic kernel FPU settings, e.g., enabling CET supervisor
>> xstate by default for guest fpstate while it's remained disabled in
>> kernel FPU config.
>> 
>> The kernel dynamic xfeatures are specifically used by guest fpstate now,
>> add the mask for guest fpstate so that guest_perm.__state_perm ==
>> (fpu_kernel_cfg.default_xfeature | XFEATURE_MASK_KERNEL_DYNAMIC). And
>> if guest fpstate is re-allocated to hold user dynamic xfeatures, the
>> resulting permissions are consumed before calculate new guest fpstate.
>
>This kinda restates what the code does, but I don't think it matches the
>code.

Actually, it does (see more below)

>
>> With new guest FPU config added, there're 3 categories of FPU configs in
>> kernel, the usages and key fields are recapped as below.
>
>This changelog is pretty rough. It's got a lot of words but not much
>substance.

Will revise the changelog.

[...]

>
>
>> 
>>   @fpu_guest_cfg.default_size
>>   - size of compacted buffer with 'fpu_guest_cfg.default_features'
>
>This looks like kerneldoc, not changelog. Are you sure you want it _here_?

No, I agree this should be a comment above fpu_guest/kernel/user_cfg.

>
>
>> @@ -829,6 +835,10 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
>>  	fpu_user_cfg.default_features = fpu_user_cfg.max_features;
>>  	fpu_user_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
>>  
>> +	fpu_guest_cfg.max_features = fpu_kernel_cfg.max_features;
>> +	fpu_guest_cfg.default_features = fpu_guest_cfg.max_features;
>> +	fpu_guest_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
>
>I thought this was saying above that it was _setting_ dynamic features.
>
>Why _not_ set them by default?

At first glance, I had the same question.

XFEATURE_MASK_*KERNEL*_DYNAMIC is not excluded here, so it is enabled by
default. I believe the confusion arises partly from the order of the
patches. I will reorder the patches as you suggested in patch 5.

Patchew 2.1-devel-b67e4c2

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