Commit eaefb447 authored by Adamos Ttofari's avatar Adamos Ttofari Committed by Yang Yingliang
Browse files

x86/fpu: Keep xfd_state in sync with MSR_IA32_XFD 

mainline inclusion
from mainline-v6.9-rc1
commit 10e4b5166df9ff7a2d5316138ca668b42d004422
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I9NZ3E

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=10e4b5166df9ff7a2d5316138ca668b42d004422



--------------------------------

Commit 67236547 ("x86/fpu: Update XFD state where required") and
commit 8bf26758 ("x86/fpu: Add XFD state to fpstate") introduced a
per CPU variable xfd_state to keep the MSR_IA32_XFD value cached, in
order to avoid unnecessary writes to the MSR.

On CPU hotplug MSR_IA32_XFD is reset to the init_fpstate.xfd, which
wipes out any stale state. But the per CPU cached xfd value is not
reset, which brings them out of sync.

As a consequence a subsequent xfd_update_state() might fail to update
the MSR which in turn can result in XRSTOR raising a #NM in kernel
space, which crashes the kernel.

To fix this, introduce xfd_set_state() to write xfd_state together
with MSR_IA32_XFD, and use it in all places that set MSR_IA32_XFD.

Fixes: 67236547 ("x86/fpu: Update XFD state where required")
Signed-off-by: default avatarAdamos Ttofari <attofari@amazon.de>
Signed-off-by: default avatarChang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240322230439.456571-1-chang.seok.bae@intel.com

Closes: https://lore.kernel.org/lkml/20230511152818.13839-1-attofari@amazon.de


Signed-off-by: default avatarYang Yingliang <yangyingliang@huawei.com>
parent 04dd32cb

arch/x86/kernel/fpu/xstate.c

+3 −2
Original line number Diff line number Diff line
@@ -176,10 +176,11 @@ void fpu__init_cpu_xstate(void) 
	 * Must happen after CR4 setup and before xsetbv() to allow KVM

	 * lazy passthrough.  Write independent of the dynamic state static

	 * key as that does not work on the boot CPU. This also ensures

	 * that any stale state is wiped out from XFD.

	 * that any stale state is wiped out from XFD. Reset the per CPU

	 * xfd cache too.

	 */

	if (cpu_feature_enabled(X86_FEATURE_XFD))

		wrmsrl(MSR_IA32_XFD, init_fpstate.xfd);

		xfd_set_state(init_fpstate.xfd);



	/*

	 * XCR_XFEATURE_ENABLED_MASK (aka. XCR0) sets user features

arch/x86/kernel/fpu/xstate.h

+10 −4
Original line number Diff line number Diff line
@@ -151,20 +151,26 @@ static inline void xfd_validate_state(struct fpstate *fpstate, u64 mask, bool rs 
#endif



#ifdef CONFIG_X86_64

static inline void xfd_set_state(u64 xfd)

{

	wrmsrl(MSR_IA32_XFD, xfd);

	__this_cpu_write(xfd_state, xfd);

}



static inline void xfd_update_state(struct fpstate *fpstate)

{

	if (fpu_state_size_dynamic()) {

		u64 xfd = fpstate->xfd;



		if (__this_cpu_read(xfd_state) != xfd) {

			wrmsrl(MSR_IA32_XFD, xfd);

			__this_cpu_write(xfd_state, xfd);

		}

		if (__this_cpu_read(xfd_state) != xfd)

			xfd_set_state(xfd);

	}

}



extern int __xfd_enable_feature(u64 which, struct fpu_guest *guest_fpu);

#else

static inline void xfd_set_state(u64 xfd) { }



static inline void xfd_update_state(struct fpstate *fpstate) { }



static inline int __xfd_enable_feature(u64 which, struct fpu_guest *guest_fpu) {