[PATCH v7 06/26] x86/fpu/xstate: Create guest fpstate with guest specific config

[Yang Weijiang]

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   | 48 ++++++++++++++++++++++++++++--------
 arch/x86/kernel/fpu/xstate.c |  2 +-
 arch/x86/kernel/fpu/xstate.h |  1 +
 3 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 516af626bf6a..985eaf8b55e0 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 +214,55 @@ 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_features includes 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.
+	 */
+	gfpstate_size = xstate_calculate_size(fpu_guest_cfg.default_features,
+					      compacted);
+
+	size = gfpstate_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
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index aa8f8595cd41..253944cb2298 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -559,7 +559,7 @@ static bool __init check_xstate_against_struct(int nr)
 	return true;
 }
 
-static unsigned int xstate_calculate_size(u64 xfeatures, bool compacted)
+unsigned int xstate_calculate_size(u64 xfeatures, bool compacted)
 {
 	unsigned int topmost = fls64(xfeatures) -  1;
 	unsigned int offset = xstate_offsets[topmost];
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 3518fb26d06b..c032acb56306 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -55,6 +55,7 @@ extern void fpu__init_cpu_xstate(void);
 extern void fpu__init_system_xstate(unsigned int legacy_size);
 
 extern void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr);
+extern unsigned int xstate_calculate_size(u64 xfeatures, bool compacted);
 
 static inline u64 xfeatures_mask_supervisor(void)
 {
-- 
2.27.0