Some issues have been reported with the for loop in stop_this_cpu() that
issues the 'wbinvd; hlt' sequence. Reverting this sequence to halt()
has been shown to resolve the issue.
However, the wbinvd is needed when running with SME. The reason for the
wbinvd is to prevent cache flush races between encrypted and non-encrypted
entries that have the same physical address. This can occur when
kexec'ing from memory encryption active to inactive or vice-versa. The
important thing is to not have outside of kernel text memory references
(such as stack usage), so the usage of the native_*() functions is needed
since these expand as inline asm sequences. So instead of reverting the
change, rework the sequence.
Move the wbinvd instruction outside of the for loop as native_wbinvd()
and make its execution conditional on X86_FEATURE_SME. In the for loop,
change the asm 'wbinvd; hlt' sequence back to a halt sequence but use
the native_halt() call.
Cc: <[email protected]> # 4.14.x
Fixes: bba4ed011a52 ("x86/mm, kexec: Allow kexec to be used with SME")
Reported-by: Dave Young <[email protected]>
Signed-off-by: Tom Lendacky <[email protected]>
---
arch/x86/kernel/process.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 63711fe..03408b9 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -379,19 +379,24 @@ void stop_this_cpu(void *dummy)
disable_local_APIC();
mcheck_cpu_clear(this_cpu_ptr(&cpu_info));
+ /*
+ * Use wbinvd on processors that support SME. This provides support
+ * for performing a successful kexec when going from SME inactive
+ * to SME active (or vice-versa). The cache must be cleared so that
+ * if there are entries with the same physical address, both with and
+ * without the encryption bit, they don't race each other when flushed
+ * and potentially end up with the wrong entry being committed to
+ * memory.
+ */
+ if (boot_cpu_has(X86_FEATURE_SME))
+ native_wbinvd();
for (;;) {
/*
- * Use wbinvd followed by hlt to stop the processor. This
- * provides support for kexec on a processor that supports
- * SME. With kexec, going from SME inactive to SME active
- * requires clearing cache entries so that addresses without
- * the encryption bit set don't corrupt the same physical
- * address that has the encryption bit set when caches are
- * flushed. To achieve this a wbinvd is performed followed by
- * a hlt. Even if the processor is not in the kexec/SME
- * scenario this only adds a wbinvd to a halting processor.
+ * Use native_halt() so that memory contents don't change
+ * (stack usage and variables) after possibly issuing the
+ * native_wbinvd() above.
*/
- asm volatile("wbinvd; hlt" : : : "memory");
+ native_halt();
}
}
On 1/17/2018 5:41 PM, Tom Lendacky wrote:
> Some issues have been reported with the for loop in stop_this_cpu() that
> issues the 'wbinvd; hlt' sequence. Reverting this sequence to halt()
> has been shown to resolve the issue.
>
> However, the wbinvd is needed when running with SME. The reason for the
> wbinvd is to prevent cache flush races between encrypted and non-encrypted
> entries that have the same physical address. This can occur when
> kexec'ing from memory encryption active to inactive or vice-versa. The
> important thing is to not have outside of kernel text memory references
> (such as stack usage), so the usage of the native_*() functions is needed
> since these expand as inline asm sequences. So instead of reverting the
> change, rework the sequence.
>
> Move the wbinvd instruction outside of the for loop as native_wbinvd()
> and make its execution conditional on X86_FEATURE_SME. In the for loop,
> change the asm 'wbinvd; hlt' sequence back to a halt sequence but use
> the native_halt() call.
>
> Cc: <[email protected]> # 4.14.x
> Fixes: bba4ed011a52 ("x86/mm, kexec: Allow kexec to be used with SME")
> Reported-by: Dave Young <[email protected]>
Dave,
Can you test this and see if it resolves your issue?
Thanks,
Tom
> Signed-off-by: Tom Lendacky <[email protected]>
> ---
> arch/x86/kernel/process.c | 25 +++++++++++++++----------
> 1 file changed, 15 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 63711fe..03408b9 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -379,19 +379,24 @@ void stop_this_cpu(void *dummy)
> disable_local_APIC();
> mcheck_cpu_clear(this_cpu_ptr(&cpu_info));
>
> + /*
> + * Use wbinvd on processors that support SME. This provides support
> + * for performing a successful kexec when going from SME inactive
> + * to SME active (or vice-versa). The cache must be cleared so that
> + * if there are entries with the same physical address, both with and
> + * without the encryption bit, they don't race each other when flushed
> + * and potentially end up with the wrong entry being committed to
> + * memory.
> + */
> + if (boot_cpu_has(X86_FEATURE_SME))
> + native_wbinvd();
> for (;;) {
> /*
> - * Use wbinvd followed by hlt to stop the processor. This
> - * provides support for kexec on a processor that supports
> - * SME. With kexec, going from SME inactive to SME active
> - * requires clearing cache entries so that addresses without
> - * the encryption bit set don't corrupt the same physical
> - * address that has the encryption bit set when caches are
> - * flushed. To achieve this a wbinvd is performed followed by
> - * a hlt. Even if the processor is not in the kexec/SME
> - * scenario this only adds a wbinvd to a halting processor.
> + * Use native_halt() so that memory contents don't change
> + * (stack usage and variables) after possibly issuing the
> + * native_wbinvd() above.
> */
> - asm volatile("wbinvd; hlt" : : : "memory");
> + native_halt();
> }
> }
>
>
On 01/17/18 at 05:47pm, Tom Lendacky wrote:
> On 1/17/2018 5:41 PM, Tom Lendacky wrote:
> > Some issues have been reported with the for loop in stop_this_cpu() that
> > issues the 'wbinvd; hlt' sequence. Reverting this sequence to halt()
> > has been shown to resolve the issue.
> >
> > However, the wbinvd is needed when running with SME. The reason for the
> > wbinvd is to prevent cache flush races between encrypted and non-encrypted
> > entries that have the same physical address. This can occur when
> > kexec'ing from memory encryption active to inactive or vice-versa. The
> > important thing is to not have outside of kernel text memory references
> > (such as stack usage), so the usage of the native_*() functions is needed
> > since these expand as inline asm sequences. So instead of reverting the
> > change, rework the sequence.
> >
> > Move the wbinvd instruction outside of the for loop as native_wbinvd()
> > and make its execution conditional on X86_FEATURE_SME. In the for loop,
> > change the asm 'wbinvd; hlt' sequence back to a halt sequence but use
> > the native_halt() call.
> >
> > Cc: <[email protected]> # 4.14.x
> > Fixes: bba4ed011a52 ("x86/mm, kexec: Allow kexec to be used with SME")
> > Reported-by: Dave Young <[email protected]>
>
> Dave,
>
> Can you test this and see if it resolves your issue?
It works for me, thank you for the patch!
Tested-by: Dave Young <[email protected]>
>
> Thanks,
> Tom
>
> > Signed-off-by: Tom Lendacky <[email protected]>
> > ---
> > arch/x86/kernel/process.c | 25 +++++++++++++++----------
> > 1 file changed, 15 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> > index 63711fe..03408b9 100644
> > --- a/arch/x86/kernel/process.c
> > +++ b/arch/x86/kernel/process.c
> > @@ -379,19 +379,24 @@ void stop_this_cpu(void *dummy)
> > disable_local_APIC();
> > mcheck_cpu_clear(this_cpu_ptr(&cpu_info));
> >
> > + /*
> > + * Use wbinvd on processors that support SME. This provides support
> > + * for performing a successful kexec when going from SME inactive
> > + * to SME active (or vice-versa). The cache must be cleared so that
> > + * if there are entries with the same physical address, both with and
> > + * without the encryption bit, they don't race each other when flushed
> > + * and potentially end up with the wrong entry being committed to
> > + * memory.
> > + */
> > + if (boot_cpu_has(X86_FEATURE_SME))
> > + native_wbinvd();
> > for (;;) {
> > /*
> > - * Use wbinvd followed by hlt to stop the processor. This
> > - * provides support for kexec on a processor that supports
> > - * SME. With kexec, going from SME inactive to SME active
> > - * requires clearing cache entries so that addresses without
> > - * the encryption bit set don't corrupt the same physical
> > - * address that has the encryption bit set when caches are
> > - * flushed. To achieve this a wbinvd is performed followed by
> > - * a hlt. Even if the processor is not in the kexec/SME
> > - * scenario this only adds a wbinvd to a halting processor.
> > + * Use native_halt() so that memory contents don't change
> > + * (stack usage and variables) after possibly issuing the
> > + * native_wbinvd() above.
> > */
> > - asm volatile("wbinvd; hlt" : : : "memory");
> > + native_halt();
> > }
> > }
> >
> >
Commit-ID: f23d74f6c66c3697e032550eeef3f640391a3a7d
Gitweb: https://git.kernel.org/tip/f23d74f6c66c3697e032550eeef3f640391a3a7d
Author: Tom Lendacky <[email protected]>
AuthorDate: Wed, 17 Jan 2018 17:41:41 -0600
Committer: Thomas Gleixner <[email protected]>
CommitDate: Thu, 18 Jan 2018 11:48:59 +0100
x86/mm: Rework wbinvd, hlt operation in stop_this_cpu()
Some issues have been reported with the for loop in stop_this_cpu() that
issues the 'wbinvd; hlt' sequence. Reverting this sequence to halt()
has been shown to resolve the issue.
However, the wbinvd is needed when running with SME. The reason for the
wbinvd is to prevent cache flush races between encrypted and non-encrypted
entries that have the same physical address. This can occur when
kexec'ing from memory encryption active to inactive or vice-versa. The
important thing is to not have outside of kernel text memory references
(such as stack usage), so the usage of the native_*() functions is needed
since these expand as inline asm sequences. So instead of reverting the
change, rework the sequence.
Move the wbinvd instruction outside of the for loop as native_wbinvd()
and make its execution conditional on X86_FEATURE_SME. In the for loop,
change the asm 'wbinvd; hlt' sequence back to a halt sequence but use
the native_halt() call.
Fixes: bba4ed011a52 ("x86/mm, kexec: Allow kexec to be used with SME")
Reported-by: Dave Young <[email protected]>
Signed-off-by: Tom Lendacky <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Dave Young <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Yu Chen <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Borislav Petkov <[email protected]>
Cc: Rui Zhang <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
---
arch/x86/kernel/process.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 832a6ac..cb368c2 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -380,19 +380,24 @@ void stop_this_cpu(void *dummy)
disable_local_APIC();
mcheck_cpu_clear(this_cpu_ptr(&cpu_info));
+ /*
+ * Use wbinvd on processors that support SME. This provides support
+ * for performing a successful kexec when going from SME inactive
+ * to SME active (or vice-versa). The cache must be cleared so that
+ * if there are entries with the same physical address, both with and
+ * without the encryption bit, they don't race each other when flushed
+ * and potentially end up with the wrong entry being committed to
+ * memory.
+ */
+ if (boot_cpu_has(X86_FEATURE_SME))
+ native_wbinvd();
for (;;) {
/*
- * Use wbinvd followed by hlt to stop the processor. This
- * provides support for kexec on a processor that supports
- * SME. With kexec, going from SME inactive to SME active
- * requires clearing cache entries so that addresses without
- * the encryption bit set don't corrupt the same physical
- * address that has the encryption bit set when caches are
- * flushed. To achieve this a wbinvd is performed followed by
- * a hlt. Even if the processor is not in the kexec/SME
- * scenario this only adds a wbinvd to a halting processor.
+ * Use native_halt() so that memory contents don't change
+ * (stack usage and variables) after possibly issuing the
+ * native_wbinvd() above.
*/
- asm volatile("wbinvd; hlt" : : : "memory");
+ native_halt();
}
}