[PATCH v9 06/27] x86/fpu/xstate: Create guest fpstate with guest specific config

Yang Weijiang
2024-01-24T02:42:35Z

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>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/kernel/fpu/core.c | 44 ++++++++++++++++++++++++++++++--------
1 file changed, 35 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 516af626bf6a..6048352e1cc7 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -194,8 +194,6 @@ 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;
@@ -216,25 +214,53 @@ 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)
{
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 = fpu_guest_cfg.default_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
--
2.39.3