x86/fpu: Remove xfd argument from __fpstate_reset()

The initial values for fpstate::xfd differ between guest and host fpstates.
Currently, the initial values are passed as an argument to
__fpstate_reset(). But, __fpstate_reset() already assigns different default
features and sizes based on the type of fpstates (i.e., guest or host). So,
handle fpstate::xfd in a similar way to highlight the differences in the
initial xfd value between guest and host fpstates

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: John Allen <john.allen@amd.com>
Link: https://lore.kernel.org/all/aBuf7wiiDT0Wflhk@google.com/
Link: https://lore.kernel.org/all/20250522151031.426788-5-chao.gao%40intel.com

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index e02705187bbf48679d94709dca374040012cf962..aefd412a23dc24d3f17916917880ea56974d4586 100644 (file)
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -218,7 +218,7 @@ void fpu_reset_from_exception_fixup(void)
 }
 
 #if IS_ENABLED(CONFIG_KVM)
-static void __fpstate_reset(struct fpstate *fpstate, u64 xfd);
+static void __fpstate_reset(struct fpstate *fpstate);
 
 static void fpu_lock_guest_permissions(void)
 {
@@ -253,8 +253,7 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
        fpstate->is_valloc      = true;
        fpstate->is_guest       = true;
 
-       /* Leave xfd to 0 (the reset value defined by spec) */
-       __fpstate_reset(fpstate, 0);
+       __fpstate_reset(fpstate);
        fpstate_init_user(fpstate);
 
        gfpu->fpstate           = fpstate;
@@ -545,7 +544,7 @@ void fpstate_init_user(struct fpstate *fpstate)
                fpstate_init_fstate(fpstate);
 }
 
-static void __fpstate_reset(struct fpstate *fpstate, u64 xfd)
+static void __fpstate_reset(struct fpstate *fpstate)
 {
        /*
         * Supervisor features (and thus sizes) may diverge between guest
@@ -553,25 +552,29 @@ static void __fpstate_reset(struct fpstate *fpstate, u64 xfd)
         * for guests despite not being utilized by the host. User
         * features and sizes are always identical, which allows for
         * common guest and userspace ABI.
+        *
+        * For the host, set XFD to the kernel's desired initialization
+        * value. For guests, set XFD to its architectural RESET value.
         */
        if (fpstate->is_guest) {
                fpstate->size           = guest_default_cfg.size;
                fpstate->xfeatures      = guest_default_cfg.features;
+               fpstate->xfd            = 0;
        } else {
                fpstate->size           = fpu_kernel_cfg.default_size;
                fpstate->xfeatures      = fpu_kernel_cfg.default_features;
+               fpstate->xfd            = init_fpstate.xfd;
        }
 
        fpstate->user_size      = fpu_user_cfg.default_size;
        fpstate->user_xfeatures = fpu_user_cfg.default_features;
-       fpstate->xfd            = xfd;
 }
 
 void fpstate_reset(struct fpu *fpu)
 {
        /* Set the fpstate pointer to the default fpstate */
        fpu->fpstate = &fpu->__fpstate;
-       __fpstate_reset(fpu->fpstate, init_fpstate.xfd);
+       __fpstate_reset(fpu->fpstate);
 
        /* Initialize the permission related info in fpu */
        fpu->perm.__state_perm          = fpu_kernel_cfg.default_features;