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Peter Anvin" , Stanislav Spassov , Eric Biggers , Oleg Nesterov , Kees Cook Subject: [PATCH v8 2/6] x86/fpu: Initialize guest FPU permissions from guest defaults Date: Thu, 22 May 2025 08:10:05 -0700 Message-ID: <20250522151031.426788-3-chao.gao@intel.com> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20250522151031.426788-1-chao.gao@intel.com> References: <20250522151031.426788-1-chao.gao@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Currently, fpu->guest_perm is copied from fpu->perm, which is derived from fpu_kernel_cfg.default_features. Guest defaults were introduced to differentiate the features and sizes of host and guest FPUs. Copying guest FPU permissions from the host will lead to inconsistencies between the guest default features and permissions. Initialize guest FPU permissions from guest defaults instead of host defaults. This ensures that any changes to guest default features are automatically reflected in guest permissions, which in turn guarantees that fpstate_realloc() allocates a correctly sized XSAVE buffer for guest FPUs. Suggested-by: Chang S. Bae Signed-off-by: Chao Gao Reviewed-by: Rick Edgecombe Reviewed-by: John Allen --- v8: Refine the comment above fpu->guest_perm.__user_state_size v6: Drop vcpu_fpu_config.user_* and collect reviews (Rick) --- arch/x86/kernel/fpu/core.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 2cd5e1910ff8..c69432d0ee41 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -553,8 +553,14 @@ void fpstate_reset(struct fpu *fpu) fpu->perm.__state_perm =3D fpu_kernel_cfg.default_features; fpu->perm.__state_size =3D fpu_kernel_cfg.default_size; fpu->perm.__user_state_size =3D fpu_user_cfg.default_size; - /* Same defaults for guests */ - fpu->guest_perm =3D fpu->perm; + + fpu->guest_perm.__state_perm =3D guest_default_cfg.features; + fpu->guest_perm.__state_size =3D guest_default_cfg.size; + /* + * User features and sizes are always identical between host and + * guest FPUs, which allows for common guest and userspace ABI. + */ + fpu->guest_perm.__user_state_size =3D fpu_user_cfg.default_size; } =20 static inline void fpu_inherit_perms(struct fpu *dst_fpu) --=20 2.47.1