[PATCH v6 06/21] x86/fpu: Add guest support to xfd_enable_feature()

Paolo Bonzini
2022-01-07T18:55:30Z

From: Thomas Gleixner <tglx@linutronix.de>

Guest support for dynamically enabled FPU features requires a few
modifications to the enablement function which is currently invoked from
the #NM handler:

1) Use guest permissions and sizes for the update

2) Update fpu_guest state accordingly

3) Take into account that the enabling can be triggered either from a
running guest via XSETBV and MSR_IA32_XFD write emulation or from
a guest restore. In the latter case the guests fpstate is not the
current tasks active fpstate.

Split the function and implement the guest mechanics throughout the
callchain.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20220105123532.12586-7-yang.zhong@intel.com>
[Add 32-bit stub for __xfd_enable_feature. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kernel/fpu/xstate.c | 93 +++++++++++++++++++++---------------
arch/x86/kernel/fpu/xstate.h | 6 +++
2 files changed, 60 insertions(+), 39 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 5f01d463859d..0c0b2323cdec 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1499,29 +1499,6 @@ void fpstate_free(struct fpu *fpu)
vfree(fpu->fpstate);
}

-/**
- * fpu_install_fpstate - Update the active fpstate in the FPU
- *
- * @fpu: A struct fpu * pointer
- * @newfps: A struct fpstate * pointer
- *
- * Returns: A null pointer if the last active fpstate is the embedded
- * one or the new fpstate is already installed;
- * otherwise, a pointer to the old fpstate which has to
- * be freed by the caller.
- */
-static struct fpstate *fpu_install_fpstate(struct fpu *fpu,
- struct fpstate *newfps)
-{
- struct fpstate *oldfps = fpu->fpstate;
-
- if (fpu->fpstate == newfps)
- return NULL;
-
- fpu->fpstate = newfps;
- return oldfps != &fpu->__fpstate ? oldfps : NULL;
-}
-
/**
* fpstate_realloc - Reallocate struct fpstate for the requested new features
*
@@ -1529,6 +1506,7 @@ static struct fpstate *fpu_install_fpstate(struct fpu *fpu,
* of that task
* @ksize: The required size for the kernel buffer
* @usize: The required size for user space buffers
+ * @guest_fpu: Pointer to a guest FPU container. NULL for host allocations
*
* Note vs. vmalloc(): If the task with a vzalloc()-allocated buffer
* terminates quickly, vfree()-induced IPIs may be a concern, but tasks
@@ -1537,13 +1515,13 @@ static struct fpstate *fpu_install_fpstate(struct fpu *fpu,
* Returns: 0 on success, -ENOMEM on allocation error.
*/
static int fpstate_realloc(u64 xfeatures, unsigned int ksize,
- unsigned int usize)
+ unsigned int usize, struct fpu_guest *guest_fpu)
{
struct fpu *fpu = &current->thread.fpu;
struct fpstate *curfps, *newfps = NULL;
unsigned int fpsize;
+ bool in_use;

- curfps = fpu->fpstate;
fpsize = ksize + ALIGN(offsetof(struct fpstate, regs), 64);

newfps = vzalloc(fpsize);
@@ -1553,28 +1531,55 @@ static int fpstate_realloc(u64 xfeatures, unsigned int ksize,
newfps->user_size = usize;
newfps->is_valloc = true;

+ /*
+ * When a guest FPU is supplied, use @guest_fpu->fpstate
+ * as reference independent whether it is in use or not.
+ */
+ curfps = guest_fpu ? guest_fpu->fpstate : fpu->fpstate;
+
+ /* Determine whether @curfps is the active fpstate */
+ in_use = fpu->fpstate == curfps;
+
+ if (guest_fpu) {
+ newfps->is_guest = true;
+ newfps->is_confidential = curfps->is_confidential;
+ newfps->in_use = curfps->in_use;
+ guest_fpu->xfeatures |= xfeatures;
+ }
+
fpregs_lock();
/*
- * Ensure that the current state is in the registers before
- * swapping fpstate as that might invalidate it due to layout
- * changes.
+ * If @curfps is in use, ensure that the current state is in the
+ * registers before swapping fpstate as that might invalidate it
+ * due to layout changes.
*/
- if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ if (in_use && test_thread_flag(TIF_NEED_FPU_LOAD))
fpregs_restore_userregs();

newfps->xfeatures = curfps->xfeatures | xfeatures;
newfps->user_xfeatures = curfps->user_xfeatures | xfeatures;
newfps->xfd = curfps->xfd & ~xfeatures;

- curfps = fpu_install_fpstate(fpu, newfps);
-
/* Do the final updates within the locked region */
xstate_init_xcomp_bv(&newfps->regs.xsave, newfps->xfeatures);
- xfd_update_state(newfps);

+ if (guest_fpu) {
+ guest_fpu->fpstate = newfps;
+ /* If curfps is active, update the FPU fpstate pointer */
+ if (in_use)
+ fpu->fpstate = newfps;
+ } else {
+ fpu->fpstate = newfps;
+ }
+
+ if (in_use)
+ xfd_update_state(fpu->fpstate);
fpregs_unlock();

- vfree(curfps);
+ /* Only free valloc'ed state */
+ if (curfps && curfps->is_valloc)
+ vfree(curfps);
+
return 0;
}

@@ -1682,14 +1687,16 @@ static int xstate_request_perm(unsigned long idx, bool guest)
return ret;
}

-int xfd_enable_feature(u64 xfd_err)
+int __xfd_enable_feature(u64 xfd_err, struct fpu_guest *guest_fpu)
{
u64 xfd_event = xfd_err & XFEATURE_MASK_USER_DYNAMIC;
+ struct fpu_state_perm *perm;
unsigned int ksize, usize;
struct fpu *fpu;

if (!xfd_event) {
- pr_err_once("XFD: Invalid xfd error: %016llx\n", xfd_err);
+ if (!guest_fpu)
+ pr_err_once("XFD: Invalid xfd error: %016llx\n", xfd_err);
return 0;
}

@@ -1697,14 +1704,16 @@ int xfd_enable_feature(u64 xfd_err)
spin_lock_irq(&current->sighand->siglock);

/* If not permitted let it die */
- if ((xstate_get_host_group_perm() & xfd_event) != xfd_event) {
+ if ((xstate_get_group_perm(!!guest_fpu) & xfd_event) != xfd_event) {
spin_unlock_irq(&current->sighand->siglock);
return -EPERM;
}

fpu = &current->group_leader->thread.fpu;
- ksize = fpu->perm.__state_size;
- usize = fpu->perm.__user_state_size;
+ perm = guest_fpu ? &fpu->guest_perm : &fpu->perm;
+ ksize = perm->__state_size;
+ usize = perm->__user_state_size;
+
/*
* The feature is permitted. State size is sufficient. Dropping
* the lock is safe here even if more features are added from
@@ -1717,10 +1726,16 @@ int xfd_enable_feature(u64 xfd_err)
* Try to allocate a new fpstate. If that fails there is no way
* out.
*/
- if (fpstate_realloc(xfd_event, ksize, usize))
+ if (fpstate_realloc(xfd_event, ksize, usize, guest_fpu))
return -EFAULT;
return 0;
}
+
+int xfd_enable_feature(u64 xfd_err)
+{
+ return __xfd_enable_feature(xfd_err, NULL);
+}
+
#else /* CONFIG_X86_64 */
static inline int xstate_request_perm(unsigned long idx, bool guest)
{
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 98a472775c97..67ed6bbc19b8 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -158,8 +158,14 @@ static inline void xfd_update_state(struct fpstate *fpstate)
}
}
}
+
+extern int __xfd_enable_feature(u64 which, struct fpu_guest *guest_fpu);
#else
static inline void xfd_update_state(struct fpstate *fpstate) { }
+
+static inline int __xfd_enable_feature(u64 which, struct fpu_guest *guest_fpu) {
+ return -EPERM;
+}
#endif

/*
--
2.31.1