[PATCH v6 5/7] x86/fpu: Initialize guest fpstate and FPU pseudo container from guest defaults

Chao Gao
2025-05-06T09:33:24Z

fpu_alloc_guest_fpstate() currently uses host defaults to initialize guest
fpstate and pseudo containers. Guest defaults were introduced to
differentiate the features and sizes of host and guest FPUs. Switch to
using guest defaults instead.

Additionally, incorporate the initialization of indicators (is_valloc and
is_guest) into the newly added guest-specific reset function to centralize
the resetting of guest fpstate.

Suggested-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
v6: Drop vcpu_fpu_config.user_* (Rick)
v5: init is_valloc/is_guest in the guest-specific reset function (Chang)
---
arch/x86/kernel/fpu/core.c | 28 ++++++++++++++++++++++------
1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 444e517a8648..78a9c809dfad 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -211,7 +211,24 @@ void fpu_reset_from_exception_fixup(void)
}

#if IS_ENABLED(CONFIG_KVM)
-static void __fpstate_reset(struct fpstate *fpstate, u64 xfd);
+static void __guest_fpstate_reset(struct fpstate *fpstate, u64 xfd)
+{
+ /*
+ * Initialize sizes and feature masks. Supervisor features and
+ * sizes may diverge between guest FPUs and host FPUs, whereas
+ * user features and sizes remain the same.
+ */
+ fpstate->size = guest_default_cfg.size;
+ fpstate->xfeatures = guest_default_cfg.features;
+ fpstate->user_size = fpu_user_cfg.default_size;
+ fpstate->user_xfeatures = fpu_user_cfg.default_features;
+ fpstate->xfd = xfd;
+
+ /* Initialize indicators to reflect properties of the fpstate */
+ fpstate->is_valloc = true;
+ fpstate->is_guest = true;
+}
+

static void fpu_lock_guest_permissions(void)
{
@@ -236,19 +253,18 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
struct fpstate *fpstate;
unsigned int size;

- size = fpu_kernel_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
+ size = guest_default_cfg.size + ALIGN(offsetof(struct fpstate, regs), 64);
+
fpstate = vzalloc(size);
if (!fpstate)
return false;

/* Leave xfd to 0 (the reset value defined by spec) */
- __fpstate_reset(fpstate, 0);
+ __guest_fpstate_reset(fpstate, 0);
fpstate_init_user(fpstate);
- fpstate->is_valloc = true;
- fpstate->is_guest = true;

gfpu->fpstate = fpstate;
- gfpu->xfeatures = fpu_kernel_cfg.default_features;
+ gfpu->xfeatures = guest_default_cfg.features;

/*
* KVM sets the FP+SSE bits in the XSAVE header when copying FPU state
--
2.47.1