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| Started by | Boris Ostrovsky <boris.ostrovsky@oracle.com> |
|---|---|
| First post | 2015-11-19 23:00 +0100 |
| Last post | 2015-11-23 17:30 +0100 |
| Articles | 2 — 2 participants |
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[PATCH v2 1/3] x86/xen: Avoid fast syscall path for Xen PV guests Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2015-11-19 23:00 +0100
[tip:x86/asm] x86/xen: Avoid fast syscall path for Xen PV guests tip-bot for Boris Ostrovsky <tipbot@zytor.com> - 2015-11-23 17:30 +0100
| From | Boris Ostrovsky <boris.ostrovsky@oracle.com> |
|---|---|
| Date | 2015-11-19 23:00 +0100 |
| Subject | [PATCH v2 1/3] x86/xen: Avoid fast syscall path for Xen PV guests |
| Message-ID | <qwFpf-6AK-7@gated-at.bofh.it> |
After 32-bit syscall rewrite, and specifically after commit 5f310f739b4c
("x86/entry/32: Re-implement SYSENTER using the new C path"), the stack
frame that is passed to xen_sysexit is no longer a "standard" one (i.e.
it's not pt_regs).
Since we end up calling xen_iret from xen_sysexit we don't need to fix
up the stack and instead follow entry_SYSENTER_32's IRET path directly
to xen_iret.
We can do the same thing for compat mode even though stack does not need
to be fixed. This will allow us to drop usergs_sysret32 paravirt op (in
the subsequent patch)
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Suggested-by: Andy Lutomirski <luto@amacapital.net>
---
arch/x86/entry/entry_32.S | 5 +++--
arch/x86/entry/entry_64_compat.S | 10 ++++++----
arch/x86/include/asm/cpufeature.h | 1 +
arch/x86/xen/enlighten.c | 4 +++-
4 files changed, 13 insertions(+), 7 deletions(-)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 3eb572e..0870825 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -308,8 +308,9 @@ sysenter_past_esp:
movl %esp, %eax
call do_fast_syscall_32
- testl %eax, %eax
- jz .Lsyscall_32_done
+ /* XEN PV guests always use IRET path */
+ ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+ "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
/* Opportunistic SYSEXIT */
TRACE_IRQS_ON /* User mode traces as IRQs on. */
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index c320183..402e34a 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -121,8 +121,9 @@ sysenter_flags_fixed:
movq %rsp, %rdi
call do_fast_syscall_32
- testl %eax, %eax
- jz .Lsyscall_32_done
+ /* XEN PV guests always use IRET path */
+ ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+ "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
jmp sysret32_from_system_call
sysenter_fix_flags:
@@ -200,8 +201,9 @@ ENTRY(entry_SYSCALL_compat)
movq %rsp, %rdi
call do_fast_syscall_32
- testl %eax, %eax
- jz .Lsyscall_32_done
+ /* XEN PV guests always use IRET path */
+ ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+ "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
/* Opportunistic SYSRET */
sysret32_from_system_call:
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index e4f8010..f7ba9fb 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -216,6 +216,7 @@
#define X86_FEATURE_PAUSEFILTER ( 8*32+13) /* AMD filtered pause intercept */
#define X86_FEATURE_PFTHRESHOLD ( 8*32+14) /* AMD pause filter threshold */
#define X86_FEATURE_VMMCALL ( 8*32+15) /* Prefer vmmcall to vmcall */
+#define X86_FEATURE_XENPV ( 8*32+16) /* "" Xen paravirtual guest */
/* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 5774800..d315151 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1886,8 +1886,10 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
static void xen_set_cpu_features(struct cpuinfo_x86 *c)
{
- if (xen_pv_domain())
+ if (xen_pv_domain()) {
clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+ set_cpu_cap(c, X86_FEATURE_XENPV);
+ }
}
const struct hypervisor_x86 x86_hyper_xen = {
--
1.8.1.4
--
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| From | tip-bot for Boris Ostrovsky <tipbot@zytor.com> |
|---|---|
| Date | 2015-11-23 17:30 +0100 |
| Subject | [tip:x86/asm] x86/xen: Avoid fast syscall path for Xen PV guests |
| Message-ID | <qy2a9-4i0-65@gated-at.bofh.it> |
| In reply to | #1273532 |
Commit-ID: 5fdf5d37f40a3b18c0d613463867f71c017b75ef
Gitweb: http://git.kernel.org/tip/5fdf5d37f40a3b18c0d613463867f71c017b75ef
Author: Boris Ostrovsky <boris.ostrovsky@oracle.com>
AuthorDate: Thu, 19 Nov 2015 16:55:45 -0500
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 23 Nov 2015 10:48:16 +0100
x86/xen: Avoid fast syscall path for Xen PV guests
After 32-bit syscall rewrite, and specifically after commit:
5f310f739b4c ("x86/entry/32: Re-implement SYSENTER using the new C path")
... the stack frame that is passed to xen_sysexit is no longer a
"standard" one (i.e. it's not pt_regs).
Since we end up calling xen_iret from xen_sysexit we don't need
to fix up the stack and instead follow entry_SYSENTER_32's IRET
path directly to xen_iret.
We can do the same thing for compat mode even though stack does
not need to be fixed. This will allow us to drop usergs_sysret32
paravirt op (in the subsequent patch)
Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: david.vrabel@citrix.com
Cc: konrad.wilk@oracle.com
Cc: virtualization@lists.linux-foundation.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1447970147-1733-2-git-send-email-boris.ostrovsky@oracle.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/entry/entry_32.S | 5 +++--
arch/x86/entry/entry_64_compat.S | 10 ++++++----
arch/x86/include/asm/cpufeature.h | 1 +
arch/x86/xen/enlighten.c | 4 +++-
4 files changed, 13 insertions(+), 7 deletions(-)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 3eb572e..0870825 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -308,8 +308,9 @@ sysenter_past_esp:
movl %esp, %eax
call do_fast_syscall_32
- testl %eax, %eax
- jz .Lsyscall_32_done
+ /* XEN PV guests always use IRET path */
+ ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+ "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
/* Opportunistic SYSEXIT */
TRACE_IRQS_ON /* User mode traces as IRQs on. */
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index c320183..402e34a 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -121,8 +121,9 @@ sysenter_flags_fixed:
movq %rsp, %rdi
call do_fast_syscall_32
- testl %eax, %eax
- jz .Lsyscall_32_done
+ /* XEN PV guests always use IRET path */
+ ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+ "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
jmp sysret32_from_system_call
sysenter_fix_flags:
@@ -200,8 +201,9 @@ ENTRY(entry_SYSCALL_compat)
movq %rsp, %rdi
call do_fast_syscall_32
- testl %eax, %eax
- jz .Lsyscall_32_done
+ /* XEN PV guests always use IRET path */
+ ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+ "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
/* Opportunistic SYSRET */
sysret32_from_system_call:
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index e4f8010..f7ba9fb 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -216,6 +216,7 @@
#define X86_FEATURE_PAUSEFILTER ( 8*32+13) /* AMD filtered pause intercept */
#define X86_FEATURE_PFTHRESHOLD ( 8*32+14) /* AMD pause filter threshold */
#define X86_FEATURE_VMMCALL ( 8*32+15) /* Prefer vmmcall to vmcall */
+#define X86_FEATURE_XENPV ( 8*32+16) /* "" Xen paravirtual guest */
/* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 5774800..d315151 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1886,8 +1886,10 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
static void xen_set_cpu_features(struct cpuinfo_x86 *c)
{
- if (xen_pv_domain())
+ if (xen_pv_domain()) {
clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+ set_cpu_cap(c, X86_FEATURE_XENPV);
+ }
}
const struct hypervisor_x86 x86_hyper_xen = {
--
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