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@xxxxxxxxx>
> ---
> 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@xxxxxxxxxx>
Best regards,
Maxim Levitsky
