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x86/fpu: Keep xfd_state in sync with MSR_IA32_XFD

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Commit 672365477ae8 ("x86/fpu: Update XFD state where required") and
commit 8bf26758ca96 ("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: 672365477ae8 ("x86/fpu: Update XFD state where required")
Signed-off-by: Adamos Ttofari <attofari@amazon.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Thomas 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
This commit is contained in:
Adamos Ttofari 2024-03-22 16:04:39 -07:00 committed by Ingo Molnar
parent a8ed59a3a8
commit 10e4b5166d
2 changed files with 13 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
arch/x86/kernel/fpu/xstate.c
View File

@ -178,10 +178,11 @@ 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

14
arch/x86/kernel/fpu/xstate.h
View File

@ -148,20 +148,26 @@ 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) {