[xen stable-4.12] x86/boot: Fix early exception handling with CONFIG_PERF_COUNTERS

[patchbot@xxxxxxx]

commit e8032787d44ff9dfe157bda9e7f47e1c58faa973
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Apr 27 15:51:14 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Apr 27 15:51:14 2020 +0200

    x86/boot: Fix early exception handling with CONFIG_PERF_COUNTERS
    
    The PERFC_INCR() macro uses current->processor, but current is not valid
    during early boot.  This causes the following crash to occur if
    e.g. rdmsr_safe() has to recover from a #GP fault.
    
      (XEN) Early fatal page fault at e008:ffff82d0803b1a39 
(cr2=0000000000000004, ec=0000)
      (XEN) ----[ Xen-4.14-unstable  x86_64  debug=y   Not tainted ]----
      (XEN) CPU:    0
      (XEN) RIP:    e008:[<ffff82d0803b1a39>] 
x86_64/entry.S#handle_exception_saved+0x64/0xb8
      ...
      (XEN) Xen call trace:
      (XEN)    [<ffff82d0803b1a39>] R 
x86_64/entry.S#handle_exception_saved+0x64/0xb8
      (XEN)    [<ffff82d0806394fe>] F __start_xen+0x2cd/0x2980
      (XEN)    [<ffff82d0802000ec>] F __high_start+0x4c/0x4e
    
    Furthermore, the PERFC_INCR() macro is wildly inefficient.  There has been a
    single caller for many releases now, so inline it and delete the macro
    completely.
    
    There is no need to reference current at all.  What is actually needed is 
the
    per_cpu_offset which can be obtained directly from the top-of-stack block.
    This simplifies the counter handling to 3 instructions and no spilling to 
the
    stack at all.
    
    The same breakage from above is now handled properly:
    
      (XEN) traps.c:1591: GPF (0000): ffff82d0806394fe 
[__start_xen+0x2cd/0x2980] -> ffff82d0803b3bfb
    
    Reported-by: Julien Grall <jgrall@xxxxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Tested-by: Julien Grall <jgrall@xxxxxxxxxx>
    master commit: 615bfe42c6d183a0e54a0525ef82b58580d01619
    master date: 2020-04-16 09:48:38 +0100
---
 xen/arch/x86/x86_64/asm-offsets.c |  1 +
 xen/arch/x86/x86_64/entry.S       |  6 +++++-
 xen/include/asm-x86/asm_defns.h   | 16 ----------------
 3 files changed, 6 insertions(+), 17 deletions(-)

diff --git a/xen/arch/x86/x86_64/asm-offsets.c 
b/xen/arch/x86/x86_64/asm-offsets.c
index 33930ce97c..5df15e26f1 100644
--- a/xen/arch/x86/x86_64/asm-offsets.c
+++ b/xen/arch/x86/x86_64/asm-offsets.c
@@ -112,6 +112,7 @@ void __dummy__(void)
     OFFSET(CPUINFO_guest_cpu_user_regs, struct cpu_info, guest_cpu_user_regs);
     OFFSET(CPUINFO_verw_sel, struct cpu_info, verw_sel);
     OFFSET(CPUINFO_current_vcpu, struct cpu_info, current_vcpu);
+    OFFSET(CPUINFO_per_cpu_offset, struct cpu_info, per_cpu_offset);
     OFFSET(CPUINFO_cr4, struct cpu_info, cr4);
     OFFSET(CPUINFO_xen_cr3, struct cpu_info, xen_cr3);
     OFFSET(CPUINFO_pv_cr3, struct cpu_info, pv_cr3);
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index e8eae3b08d..94d9a51a17 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -682,7 +682,11 @@ handle_exception_saved:
 1:      movq  %rsp,%rdi
         movzbl UREGS_entry_vector(%rsp),%eax
         leaq  exception_table(%rip),%rdx
-        PERFC_INCR(exceptions, %rax, %rbx)
+#ifdef CONFIG_PERF_COUNTERS
+        lea   per_cpu__perfcounters(%rip), %rcx
+        add   STACK_CPUINFO_FIELD(per_cpu_offset)(%r14), %rcx
+        incl  ASM_PERFC_exceptions * 4(%rcx, %rax, 4)
+#endif
         mov   (%rdx, %rax, 8), %rdx
         INDIRECT_CALL %rdx
         mov   %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
diff --git a/xen/include/asm-x86/asm_defns.h b/xen/include/asm-x86/asm_defns.h
index e688cf1c16..1364a14b98 100644
--- a/xen/include/asm-x86/asm_defns.h
+++ b/xen/include/asm-x86/asm_defns.h
@@ -334,22 +334,6 @@ static always_inline void stac(void)
 
 #endif
 
-#ifdef CONFIG_PERF_COUNTERS
-#define PERFC_INCR(_name,_idx,_cur)             \
-        pushq _cur;                             \
-        movslq VCPU_processor(_cur),_cur;       \
-        pushq %rdx;                             \
-        leaq __per_cpu_offset(%rip),%rdx;       \
-        movq (%rdx,_cur,8),_cur;                \
-        leaq per_cpu__perfcounters(%rip),%rdx;  \
-        addq %rdx,_cur;                         \
-        popq %rdx;                              \
-        incl ASM_PERFC_##_name*4(_cur,_idx,4);  \
-        popq _cur
-#else
-#define PERFC_INCR(_name,_idx,_cur)
-#endif
-
 /* Work around AMD erratum #88 */
 #define safe_swapgs                             \
         "mfence; swapgs;"
--
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