The following commit has been merged into the x86/fpu branch of tip:
Commit-ID: dda366083e5ff307a4a728757db874bbfe7550be
Gitweb: https://git.kernel.org/tip/dda366083e5ff307a4a728757db874bbfe7550be
Author: Chao Gao <chao.gao@xxxxxxxxx>
AuthorDate: Mon, 17 Mar 2025 22:06:11 +08:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Mon, 17 Mar 2025 23:52:31 +01:00
x86/fpu/xstate: Fix inconsistencies in guest FPU xfeatures
Guest FPUs manage vCPU FPU states. They are allocated via
fpu_alloc_guest_fpstate() and are resized in fpstate_realloc() when XFD
features are enabled.
Since the introduction of guest FPUs, there have been inconsistencies in
the kernel buffer size and xfeatures:
1. fpu_alloc_guest_fpstate() uses fpu_user_cfg since its introduction. See:
69f6ed1d14c6 ("x86/fpu: Provide infrastructure for KVM FPU cleanup")
36487e6228c4 ("x86/fpu: Prepare guest FPU for dynamically enabled FPU features")
2. __fpstate_reset() references fpu_kernel_cfg to set storage attributes.
3. fpu->guest_perm uses fpu_kernel_cfg, affecting fpstate_realloc().
A recent commit in the tip:x86/fpu tree partially addressed the inconsistency
between (1) and (3) by using fpu_kernel_cfg for size calculation in (1),
but left fpu_guest->xfeatures and fpu_guest->perm still referencing
fpu_user_cfg:
https://lore.kernel.org/all/20250218141045.85201-1-stanspas@xxxxxxxxx/
1937e18cc3cf ("x86/fpu: Fix guest FPU state buffer allocation size")
The inconsistencies within fpu_alloc_guest_fpstate() and across the
mentioned functions cause confusion.
Fix them by using fpu_kernel_cfg consistently in fpu_alloc_guest_fpstate(),
except for fields related to the UABI buffer. Referencing fpu_kernel_cfg
won't impact functionalities, as:
1. fpu_guest->perm is overwritten shortly in fpu_init_guest_permissions()
with fpstate->guest_perm, which already uses fpu_kernel_cfg.
2. fpu_guest->xfeatures is solely used to check if XFD features are enabled.
Including supervisor xfeatures doesn't affect the check.
Fixes: 36487e6228c4 ("x86/fpu: Prepare guest FPU for dynamically enabled FPU features")
Suggested-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250317140613.1761633-1-chao.gao@xxxxxxxxx
---
arch/x86/kernel/fpu/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 422c98c..1b734a9 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -239,8 +239,8 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
fpstate->is_guest = true;
gfpu->fpstate = fpstate;
- gfpu->xfeatures = fpu_user_cfg.default_features;
- gfpu->perm = fpu_user_cfg.default_features;
+ gfpu->xfeatures = fpu_kernel_cfg.default_features;
+ gfpu->perm = fpu_kernel_cfg.default_features;
/*
* KVM sets the FP+SSE bits in the XSAVE header when copying FPU state
|