2023-09-14 17:31:23

by Yang Weijiang

Subject: [PATCH v6 05/25] x86/fpu/xstate: Remove kernel dynamic xfeatures from kernel default_features

The kernel dynamic xfeatures are supported by host, i.e., they're enabled
in xsaves/xrstors operating xfeature set (XCR0 | XSS), but the corresponding
CPU features are disabled for the time-being in host kernel so the bits are
not necessarily set by default.

Remove the bits from fpu_kernel_cfg.default_features so that the bits in
xstate_bv and xcomp_bv are cleared and xsaves/xrstors can be optimized by HW
for normal fpstate.

Signed-off-by: Yang Weijiang <[email protected]>
---
arch/x86/kernel/fpu/xstate.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index eaec05bc1b3c..4753c677e2e1 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -845,6 +845,7 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
/* Clean out dynamic features from default */
fpu_kernel_cfg.default_features = fpu_kernel_cfg.max_features;
fpu_kernel_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
+ fpu_kernel_cfg.default_features &= ~fpu_kernel_dynamic_xfeatures;

fpu_user_cfg.default_features = fpu_user_cfg.max_features;
fpu_user_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
--
2.27.0

2023-09-14 19:07:24

by Dave Hansen

Subject: Re: [PATCH v6 05/25] x86/fpu/xstate: Remove kernel dynamic xfeatures from kernel default_features

On 9/13/23 23:33, Yang Weijiang wrote:
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -845,6 +845,7 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
> /* Clean out dynamic features from default */
> fpu_kernel_cfg.default_features = fpu_kernel_cfg.max_features;
> fpu_kernel_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
> + fpu_kernel_cfg.default_features &= ~fpu_kernel_dynamic_xfeatures;

I'd much rather that this be a closer analog to XFEATURE_MASK_USER_DYNAMIC.

Please define a XFEATURE_MASK_KERNEL_DYNAMIC value and use it here.
Don't use a dynamically generated one.

2023-09-15 10:11:04

by Yang Weijiang

Subject: Re: [PATCH v6 05/25] x86/fpu/xstate: Remove kernel dynamic xfeatures from kernel default_features

On 9/15/2023 12:22 AM, Dave Hansen wrote:
> On 9/13/23 23:33, Yang Weijiang wrote:
>> --- a/arch/x86/kernel/fpu/xstate.c
>> +++ b/arch/x86/kernel/fpu/xstate.c
>> @@ -845,6 +845,7 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
>> /* Clean out dynamic features from default */
>> fpu_kernel_cfg.default_features = fpu_kernel_cfg.max_features;
>> fpu_kernel_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
>> + fpu_kernel_cfg.default_features &= ~fpu_kernel_dynamic_xfeatures;
> I'd much rather that this be a closer analog to XFEATURE_MASK_USER_DYNAMIC.
>
> Please define a XFEATURE_MASK_KERNEL_DYNAMIC value and use it here.
> Don't use a dynamically generated one.

OK,  I will change it, thanks!

2023-10-31 17:46:14

by Maxim Levitsky

Subject: Re: [PATCH v6 05/25] x86/fpu/xstate: Remove kernel dynamic xfeatures from kernel default_features

On Thu, 2023-09-14 at 09:22 -0700, Dave Hansen wrote:
> On 9/13/23 23:33, Yang Weijiang wrote:
> > --- a/arch/x86/kernel/fpu/xstate.c
> > +++ b/arch/x86/kernel/fpu/xstate.c
> > @@ -845,6 +845,7 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
> > /* Clean out dynamic features from default */
> > fpu_kernel_cfg.default_features = fpu_kernel_cfg.max_features;
> > fpu_kernel_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
> > + fpu_kernel_cfg.default_features &= ~fpu_kernel_dynamic_xfeatures;
>
> I'd much rather that this be a closer analog to XFEATURE_MASK_USER_DYNAMIC.
>
> Please define a XFEATURE_MASK_KERNEL_DYNAMIC value and use it here.
> Don't use a dynamically generated one.
>

I also think so.

Best regards,
Maxim Levitsky