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Message-ID: <20230519112315.30616-1-attofari@amazon.de>
Date: Fri, 19 May 2023 11:23:12 +0000
From: Adamos Ttofari <attofari@...zon.de>
To: <chang.seok.bae@...el.com>, <tglx@...utronix.de>
CC: <attofari@...zon.de>, <abusse@...zon.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>, Kyle Huey <me@...ehuey.com>,
Andrew Cooper <andrew.cooper3@...rix.com>,
<linux-kernel@...r.kernel.org>
Subject: [PATCH v3] x86: fpu: Keep xfd_state always in sync with MSR_IA32_XFD
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 address the issue mentioned, initialize xfd_state together with
MSR_IA32_XFD.
Fixes: 672365477ae8 ("x86/fpu: Update XFD state where required")
Signed-off-by: Adamos Ttofari <attofari@...zon.de>
---
arch/x86/kernel/fpu/xstate.c | 5 +++--
arch/x86/kernel/fpu/xstate.h | 14 ++++++++++----
2 files changed, 13 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 0bab497c9436..9bff4f07358d 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -177,10 +177,11 @@ 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
diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index a4ecb04d8d64..d272fc214113 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -147,20 +147,26 @@ 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) {
--
2.39.2
Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879
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