diff mbox series

[v8,06/26] x86/fpu/xstate: Create guest fpstate with guest specific config

Message ID 20231221140239.4349-7-weijiang.yang@intel.com
State New
Headers
Series Enable CET Virtualization |

Commit Message

Yang, Weijiang Dec. 21, 2023, 2:02 p.m. UTC 
  Use fpu_guest_cfg to calculate guest fpstate settings, open code for
__fpstate_reset() to avoid using kernel FPU config.

Below configuration steps are currently enforced to get guest fpstate:
1) Kernel sets up guest FPU settings in fpu__init_system_xstate().
2) User space sets vCPU thread group xstate permits via arch_prctl().
3) User space creates guest fpstate via __fpu_alloc_init_guest_fpstate()
   for vcpu thread.
4) User space enables guest dynamic xfeatures and re-allocate guest
   fpstate.

By adding kernel dynamic xfeatures in above #1 and #2, guest xstate area
size is expanded to hold (fpu_kernel_cfg.default_features | kernel dynamic
xfeatures | user dynamic xfeatures), then host xsaves/xrstors can operate
for all guest xfeatures.

The user_* fields remain unchanged for compatibility with KVM uAPIs.

Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
 arch/x86/kernel/fpu/core.c | 47 ++++++++++++++++++++++++++++++--------
 1 file changed, 37 insertions(+), 10 deletions(-)

Comments

Maxim Levitsky Jan. 2, 2024, 10:32 p.m. UTC | #1 
On Thu, 2023-12-21 at 09:02 -0500, Yang Weijiang wrote:
> Use fpu_guest_cfg to calculate guest fpstate settings, open code for
> __fpstate_reset() to avoid using kernel FPU config.
> 
> Below configuration steps are currently enforced to get guest fpstate:
> 1) Kernel sets up guest FPU settings in fpu__init_system_xstate().
> 2) User space sets vCPU thread group xstate permits via arch_prctl().
> 3) User space creates guest fpstate via __fpu_alloc_init_guest_fpstate()
>    for vcpu thread.
> 4) User space enables guest dynamic xfeatures and re-allocate guest
>    fpstate.
> 
> By adding kernel dynamic xfeatures in above #1 and #2, guest xstate area
> size is expanded to hold (fpu_kernel_cfg.default_features | kernel dynamic
> xfeatures | user dynamic xfeatures), then host xsaves/xrstors can operate
> for all guest xfeatures.
> 
> The user_* fields remain unchanged for compatibility with KVM uAPIs.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
>  arch/x86/kernel/fpu/core.c | 47 ++++++++++++++++++++++++++++++--------
>  1 file changed, 37 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> index 976f519721e2..0e0bf151418f 100644
> --- a/arch/x86/kernel/fpu/core.c
> +++ b/arch/x86/kernel/fpu/core.c
> @@ -250,8 +250,6 @@ void fpu_reset_from_exception_fixup(void)
>  }
>  
>  #if IS_ENABLED(CONFIG_KVM)
> -static void __fpstate_reset(struct fpstate *fpstate, u64 xfd);
> -
>  static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
>  {
>  	struct fpu_state_perm *fpuperm;
> @@ -272,25 +270,54 @@ static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
>  	gfpu->perm = perm & ~FPU_GUEST_PERM_LOCKED;
>  }
>  
> -bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
> +static struct fpstate *__fpu_alloc_init_guest_fpstate(struct fpu_guest *gfpu)
>  {
> +	bool compacted = cpu_feature_enabled(X86_FEATURE_XCOMPACTED);
> +	unsigned int gfpstate_size, size;
>  	struct fpstate *fpstate;
> -	unsigned int size;
>  
> -	size = fpu_user_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
> +	/*
> +	 * fpu_guest_cfg.default_size is initialized to hold all enabled
> +	 * xfeatures except the user dynamic xfeatures. If the user dynamic
> +	 * xfeatures are enabled, the guest fpstate will be re-allocated to
> +	 * hold all guest enabled xfeatures, so omit user dynamic xfeatures
> +	 * here.
> +	 */
> +	size = fpu_guest_cfg.default_size +
> +	       ALIGN(offsetof(struct fpstate, regs), 64);
> +
>  	fpstate = vzalloc(size);
>  	if (!fpstate)
> -		return false;
> +		return NULL;
> +	/*
> +	 * Initialize sizes and feature masks, use fpu_user_cfg.*
> +	 * for user_* settings for compatibility of exiting uAPIs.
> +	 */
> +	fpstate->size		= gfpstate_size;
> +	fpstate->xfeatures	= fpu_guest_cfg.default_features;
> +	fpstate->user_size	= fpu_user_cfg.default_size;
> +	fpstate->user_xfeatures	= fpu_user_cfg.default_features;
> +	fpstate->xfd		= 0;
>  
> -	/* Leave xfd to 0 (the reset value defined by spec) */
> -	__fpstate_reset(fpstate, 0);
>  	fpstate_init_user(fpstate);
>  	fpstate->is_valloc	= true;
>  	fpstate->is_guest	= true;
>  
>  	gfpu->fpstate		= fpstate;
> -	gfpu->xfeatures		= fpu_user_cfg.default_features;
> -	gfpu->perm		= fpu_user_cfg.default_features;
> +	gfpu->xfeatures		= fpu_guest_cfg.default_features;
> +	gfpu->perm		= fpu_guest_cfg.default_features;
> +
> +	return fpstate;
> +}
> +
> +bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
> +{
> +	struct fpstate *fpstate;
> +
> +	fpstate = __fpu_alloc_init_guest_fpstate(gfpu);
> +
> +	if (!fpstate)
> +		return false;
>  
>  	/*
>  	 * KVM sets the FP+SSE bits in the XSAVE header when copying FPU state

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
	Maxim Levitsky
Edgecombe, Rick P Jan. 3, 2024, 6:16 p.m. UTC | #2 
On Thu, 2023-12-21 at 09:02 -0500, Yang Weijiang wrote:
>  #if IS_ENABLED(CONFIG_KVM)
> -static void __fpstate_reset(struct fpstate *fpstate, u64 xfd);
> -
>  static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
>  {
>         struct fpu_state_perm *fpuperm;
> @@ -272,25 +270,54 @@ static void fpu_init_guest_permissions(struct
> fpu_guest *gfpu)
>         gfpu->perm = perm & ~FPU_GUEST_PERM_LOCKED;
>  }
>  
> -bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
> +static struct fpstate *__fpu_alloc_init_guest_fpstate(struct
> fpu_guest *gfpu)
>  {
> +       bool compacted = cpu_feature_enabled(X86_FEATURE_XCOMPACTED);

With CONFIG_WERROR I get:
arch/x86/kernel/fpu/core.c: In function
‘__fpu_alloc_init_guest_fpstate’:
arch/x86/kernel/fpu/core.c:275:14: error: unused variable ‘compacted’
[-Werror=unused-variable]
275 |         bool compacted =
cpu_feature_enabled(X86_FEATURE_XCOMPACTED);
Yang, Weijiang Jan. 4, 2024, 2:16 a.m. UTC | #3 
On 1/4/2024 2:16 AM, Edgecombe, Rick P wrote:
> On Thu, 2023-12-21 at 09:02 -0500, Yang Weijiang wrote:
>>   #if IS_ENABLED(CONFIG_KVM)
>> -static void __fpstate_reset(struct fpstate *fpstate, u64 xfd);
>> -
>>   static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
>>   {
>>          struct fpu_state_perm *fpuperm;
>> @@ -272,25 +270,54 @@ static void fpu_init_guest_permissions(struct
>> fpu_guest *gfpu)
>>          gfpu->perm = perm & ~FPU_GUEST_PERM_LOCKED;
>>   }
>>   
>> -bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
>> +static struct fpstate *__fpu_alloc_init_guest_fpstate(struct
>> fpu_guest *gfpu)
>>   {
>> +       bool compacted = cpu_feature_enabled(X86_FEATURE_XCOMPACTED);
> With CONFIG_WERROR I get:
> arch/x86/kernel/fpu/core.c: In function
> ‘__fpu_alloc_init_guest_fpstate’:
> arch/x86/kernel/fpu/core.c:275:14: error: unused variable ‘compacted’
> [-Werror=unused-variable]
> 275 |         bool compacted =
> cpu_feature_enabled(X86_FEATURE_XCOMPACTED);

Nice catch! Will remove this unused variable, thanks!

>
Edgecombe, Rick P Jan. 4, 2024, 10:47 p.m. UTC | #4 
On Thu, 2023-12-21 at 09:02 -0500, Yang Weijiang wrote:
> +static struct fpstate *__fpu_alloc_init_guest_fpstate(struct
> fpu_guest *gfpu)
>  {
> +       bool compacted = cpu_feature_enabled(X86_FEATURE_XCOMPACTED);
> +       unsigned int gfpstate_size, size;
>         struct fpstate *fpstate;
> -       unsigned int size;
>  
> -       size = fpu_user_cfg.default_size + ALIGN(offsetof(struct
> fpstate, regs), 64);
> +       /*
> +        * fpu_guest_cfg.default_size is initialized to hold all
> enabled
> +        * xfeatures except the user dynamic xfeatures. If the user
> dynamic
> +        * xfeatures are enabled, the guest fpstate will be re-
> allocated to
> +        * hold all guest enabled xfeatures, so omit user dynamic
> xfeatures
> +        * here.
> +        */
> +       size = fpu_guest_cfg.default_size +
> +              ALIGN(offsetof(struct fpstate, regs), 64);
> +
>         fpstate = vzalloc(size);
>         if (!fpstate)
> -               return false;
> +               return NULL;
> +       /*
> +        * Initialize sizes and feature masks, use fpu_user_cfg.*
> +        * for user_* settings for compatibility of exiting uAPIs.
> +        */
> +       fpstate->size           = gfpstate_size;

gfpstate_size is used uninitialized.
Yang, Weijiang Jan. 5, 2024, 8:16 a.m. UTC | #5 
On 1/5/2024 6:47 AM, Edgecombe, Rick P wrote:
> On Thu, 2023-12-21 at 09:02 -0500, Yang Weijiang wrote:
>> +static struct fpstate *__fpu_alloc_init_guest_fpstate(struct
>> fpu_guest *gfpu)
>>   {
>> +       bool compacted = cpu_feature_enabled(X86_FEATURE_XCOMPACTED);
>> +       unsigned int gfpstate_size, size;
>>          struct fpstate *fpstate;
>> -       unsigned int size;
>>   
>> -       size = fpu_user_cfg.default_size + ALIGN(offsetof(struct
>> fpstate, regs), 64);
>> +       /*
>> +        * fpu_guest_cfg.default_size is initialized to hold all
>> enabled
>> +        * xfeatures except the user dynamic xfeatures. If the user
>> dynamic
>> +        * xfeatures are enabled, the guest fpstate will be re-
>> allocated to
>> +        * hold all guest enabled xfeatures, so omit user dynamic
>> xfeatures
>> +        * here.
>> +        */
>> +       size = fpu_guest_cfg.default_size +
>> +              ALIGN(offsetof(struct fpstate, regs), 64);
>> +
>>          fpstate = vzalloc(size);
>>          if (!fpstate)
>> -               return false;
>> +               return NULL;
>> +       /*
>> +        * Initialize sizes and feature masks, use fpu_user_cfg.*
>> +        * for user_* settings for compatibility of exiting uAPIs.
>> +        */
>> +       fpstate->size           = gfpstate_size;
> gfpstate_size is used uninitialized.

Ah, this is another unused variable after introduce fpu_guest_cfg.*, should be replaced by
fpu_guest_cfg.default_size. Thanks for caching it!
diff mbox series

Patch

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 976f519721e2..0e0bf151418f 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -250,8 +250,6 @@  void fpu_reset_from_exception_fixup(void)
 }
 
 #if IS_ENABLED(CONFIG_KVM)
-static void __fpstate_reset(struct fpstate *fpstate, u64 xfd);
-
 static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
 {
 	struct fpu_state_perm *fpuperm;
@@ -272,25 +270,54 @@  static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
 	gfpu->perm = perm & ~FPU_GUEST_PERM_LOCKED;
 }
 
-bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
+static struct fpstate *__fpu_alloc_init_guest_fpstate(struct fpu_guest *gfpu)
 {
+	bool compacted = cpu_feature_enabled(X86_FEATURE_XCOMPACTED);
+	unsigned int gfpstate_size, size;
 	struct fpstate *fpstate;
-	unsigned int size;
 
-	size = fpu_user_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
+	/*
+	 * fpu_guest_cfg.default_size is initialized to hold all enabled
+	 * xfeatures except the user dynamic xfeatures. If the user dynamic
+	 * xfeatures are enabled, the guest fpstate will be re-allocated to
+	 * hold all guest enabled xfeatures, so omit user dynamic xfeatures
+	 * here.
+	 */
+	size = fpu_guest_cfg.default_size +
+	       ALIGN(offsetof(struct fpstate, regs), 64);
+
 	fpstate = vzalloc(size);
 	if (!fpstate)
-		return false;
+		return NULL;
+	/*
+	 * Initialize sizes and feature masks, use fpu_user_cfg.*
+	 * for user_* settings for compatibility of exiting uAPIs.
+	 */
+	fpstate->size		= gfpstate_size;
+	fpstate->xfeatures	= fpu_guest_cfg.default_features;
+	fpstate->user_size	= fpu_user_cfg.default_size;
+	fpstate->user_xfeatures	= fpu_user_cfg.default_features;
+	fpstate->xfd		= 0;
 
-	/* Leave xfd to 0 (the reset value defined by spec) */
-	__fpstate_reset(fpstate, 0);
 	fpstate_init_user(fpstate);
 	fpstate->is_valloc	= true;
 	fpstate->is_guest	= true;
 
 	gfpu->fpstate		= fpstate;
-	gfpu->xfeatures		= fpu_user_cfg.default_features;
-	gfpu->perm		= fpu_user_cfg.default_features;
+	gfpu->xfeatures		= fpu_guest_cfg.default_features;
+	gfpu->perm		= fpu_guest_cfg.default_features;
+
+	return fpstate;
+}
+
+bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
+{
+	struct fpstate *fpstate;
+
+	fpstate = __fpu_alloc_init_guest_fpstate(gfpu);
+
+	if (!fpstate)
+		return false;
 
 	/*
 	 * KVM sets the FP+SSE bits in the XSAVE header when copying FPU state