[PATCH 4/9] x86/pv: Implement pv_hypercall() in C

[Andrew Cooper <andrew.cooper3@citrix.com>]

In a similar style to hvm_do_hypercall().  The C version is far easier to
understand and edit than the assembly versions.

There are a few small differences however.  The register clobbering values
have changed (to match the HVM side), and in particular clobber the upper
32bits of 64bit arguments.  The hypercall and performance counter record are
reordered to increase code sharing between the 32bit and 64bit cases.

The sole callers of __trace_hypercall_entry() were the assembly code.  Given
the new C layout, it is more convenient to fold __trace_hypercall_entry() into
pv_hypercall(), and call __trace_hypercall() directly.

Finally, pv_hypercall() will treat a NULL hypercall function pointer as
-ENOSYS, allowing further cleanup.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
---
 xen/arch/x86/hypercall.c           | 115 +++++++++++++++++++++++++++++++++++++
 xen/arch/x86/trace.c               |  27 ---------
 xen/arch/x86/x86_64/asm-offsets.c  |   1 -
 xen/arch/x86/x86_64/compat/entry.S |  68 +---------------------
 xen/arch/x86/x86_64/entry.S        |  60 +------------------
 5 files changed, 119 insertions(+), 152 deletions(-)

diff --git a/xen/arch/x86/hypercall.c b/xen/arch/x86/hypercall.c
index 4b42f86..2dc787e 100644
--- a/xen/arch/x86/hypercall.c
+++ b/xen/arch/x86/hypercall.c
@@ -17,7 +17,9 @@
  * Copyright (c) 2015,2016 Citrix Systems Ltd.
  */
 
+#include <xen/compiler.h>
 #include <xen/hypercall.h>
+#include <xen/trace.h>
 
 #define ARGS(x, n)                              \
     [ __HYPERVISOR_ ## x ] = (n)
@@ -111,6 +113,119 @@ const uint8_t compat_hypercall_args_table[NR_hypercalls] =
 
 #undef ARGS
 
+long pv_hypercall(struct cpu_user_regs *regs)
+{
+    struct vcpu *curr = current;
+#ifndef NDEBUG
+    unsigned long old_rip = regs->rip;
+#endif
+    long ret;
+    uint32_t eax = regs->eax;
+
+    ASSERT(curr->arch.flags & TF_kernel_mode);
+
+    if ( (eax >= NR_hypercalls) || !hypercall_table[eax] )
+         return -ENOSYS;
+
+    if ( !is_pv_32bit_vcpu(curr) )
+    {
+        unsigned long rdi = regs->rdi;
+        unsigned long rsi = regs->rsi;
+        unsigned long rdx = regs->rdx;
+        unsigned long r10 = regs->r10;
+        unsigned long r8 = regs->r8;
+        unsigned long r9 = regs->r9;
+
+#ifndef NDEBUG
+        /* Deliberately corrupt parameter regs not used by this hypercall. */
+        switch ( hypercall_args_table[eax] )
+        {
+        case 0: rdi = 0xdeadbeefdeadf00dUL;
+        case 1: rsi = 0xdeadbeefdeadf00dUL;
+        case 2: rdx = 0xdeadbeefdeadf00dUL;
+        case 3: r10 = 0xdeadbeefdeadf00dUL;
+        case 4: r8 = 0xdeadbeefdeadf00dUL;
+        case 5: r9 = 0xdeadbeefdeadf00dUL;
+        }
+#endif
+        if ( unlikely(tb_init_done) )
+        {
+            unsigned long args[6] = { rdi, rsi, rdx, r10, r8, r9 };
+
+            __trace_hypercall(TRC_PV_HYPERCALL_V2, eax, args);
+        }
+
+        ret = hypercall_table[eax](rdi, rsi, rdx, r10, r8, r9);
+
+#ifndef NDEBUG
+        if ( regs->rip == old_rip )
+        {
+            /* Deliberately corrupt parameter regs used by this hypercall. */
+            switch ( hypercall_args_table[eax] )
+            {
+            case 6: regs->r9  = 0xdeadbeefdeadf00dUL;
+            case 5: regs->r8  = 0xdeadbeefdeadf00dUL;
+            case 4: regs->r10 = 0xdeadbeefdeadf00dUL;
+            case 3: regs->edx = 0xdeadbeefdeadf00dUL;
+            case 2: regs->esi = 0xdeadbeefdeadf00dUL;
+            case 1: regs->edi = 0xdeadbeefdeadf00dUL;
+            }
+        }
+#endif
+    }
+    else
+    {
+        unsigned int ebx = regs->_ebx;
+        unsigned int ecx = regs->_ecx;
+        unsigned int edx = regs->_edx;
+        unsigned int esi = regs->_esi;
+        unsigned int edi = regs->_edi;
+        unsigned int ebp = regs->_ebp;
+
+#ifndef NDEBUG
+        /* Deliberately corrupt parameter regs not used by this hypercall. */
+        switch ( compat_hypercall_args_table[eax] )
+        {
+        case 0: ebx = 0xdeadf00d;
+        case 1: ecx = 0xdeadf00d;
+        case 2: edx = 0xdeadf00d;
+        case 3: esi = 0xdeadf00d;
+        case 4: edi = 0xdeadf00d;
+        case 5: ebp = 0xdeadf00d;
+        }
+#endif
+
+        if ( unlikely(tb_init_done) )
+        {
+            unsigned long args[6] = { ebx, ecx, edx, esi, edi, ebp };
+
+            __trace_hypercall(TRC_PV_HYPERCALL_V2, eax, args);
+        }
+
+        ret = compat_hypercall_table[eax](ebx, ecx, edx, esi, edi, ebp);
+
+#ifndef NDEBUG
+        if ( regs->rip == old_rip )
+        {
+            /* Deliberately corrupt parameter regs used by this hypercall. */
+            switch ( compat_hypercall_args_table[eax] )
+            {
+            case 6: regs->ebp = 0xdeadf00d;
+            case 5: regs->edi = 0xdeadf00d;
+            case 4: regs->esi = 0xdeadf00d;
+            case 3: regs->edx = 0xdeadf00d;
+            case 2: regs->ecx = 0xdeadf00d;
+            case 1: regs->ebx = 0xdeadf00d;
+            }
+        }
+#endif
+    }
+
+    perfc_incr(hypercalls);
+
+    return ret;
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/x86/trace.c b/xen/arch/x86/trace.c
index bd8596c..f11b309 100644
--- a/xen/arch/x86/trace.c
+++ b/xen/arch/x86/trace.c
@@ -6,33 +6,6 @@
 #include <xen/sched.h>
 #include <xen/trace.h>
 
-void __trace_hypercall_entry(void)
-{
-    struct cpu_user_regs *regs = guest_cpu_user_regs();
-    unsigned long args[6];
-
-    if ( is_pv_32bit_vcpu(current) )
-    {
-        args[0] = regs->ebx;
-        args[1] = regs->ecx;
-        args[2] = regs->edx;
-        args[3] = regs->esi;
-        args[4] = regs->edi;
-        args[5] = regs->ebp;
-    }
-    else
-    {
-        args[0] = regs->rdi;
-        args[1] = regs->rsi;
-        args[2] = regs->rdx;
-        args[3] = regs->r10;
-        args[4] = regs->r8;
-        args[5] = regs->r9;
-    }
-
-    __trace_hypercall(TRC_PV_HYPERCALL_V2, regs->eax, args);
-}
-
 void __trace_pv_trap(int trapnr, unsigned long eip,
                      int use_error_code, unsigned error_code)
 {
diff --git a/xen/arch/x86/x86_64/asm-offsets.c b/xen/arch/x86/x86_64/asm-offsets.c
index 05d2b85..64905c6 100644
--- a/xen/arch/x86/x86_64/asm-offsets.c
+++ b/xen/arch/x86/x86_64/asm-offsets.c
@@ -153,7 +153,6 @@ void __dummy__(void)
     BLANK();
 
 #ifdef CONFIG_PERF_COUNTERS
-    DEFINE(ASM_PERFC_hypercalls, PERFC_hypercalls);
     DEFINE(ASM_PERFC_exceptions, PERFC_exceptions);
     BLANK();
 #endif
diff --git a/xen/arch/x86/x86_64/compat/entry.S b/xen/arch/x86/x86_64/compat/entry.S
index 1a8e085..521af48 100644
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -25,70 +25,10 @@ UNLIKELY_START(ne, msi_check)
         LOAD_C_CLOBBERED compat=1 ax=0
 UNLIKELY_END(msi_check)
 
-        movl  UREGS_rax(%rsp),%eax
         GET_CURRENT(bx)
 
-        cmpl  $NR_hypercalls,%eax
-        jae   compat_bad_hypercall
-#ifndef NDEBUG
-        /* Deliberately corrupt parameter regs not used by this hypercall. */
-        pushq UREGS_rbx(%rsp); pushq %rcx; pushq %rdx; pushq %rsi; pushq %rdi
-        pushq UREGS_rbp+5*8(%rsp)
-        leaq  compat_hypercall_args_table(%rip),%r10
-        movl  $6,%ecx
-        subb  (%r10,%rax,1),%cl
-        movq  %rsp,%rdi
-        movl  $0xDEADBEEF,%eax
-        rep   stosq
-        popq  %r8 ; popq  %r9 ; xchgl %r8d,%r9d /* Args 5&6: zero extend */
-        popq  %rdx; popq  %rcx; xchgl %edx,%ecx /* Args 3&4: zero extend */
-        popq  %rdi; popq  %rsi; xchgl %edi,%esi /* Args 1&2: zero extend */
-        movl  UREGS_rax(%rsp),%eax
-        pushq %rax
-        pushq UREGS_rip+8(%rsp)
-#define SHADOW_BYTES 16 /* Shadow EIP + shadow hypercall # */
-#else
-        /* Relocate argument registers and zero-extend to 64 bits. */
-        xchgl %ecx,%esi              /* Arg 2, Arg 4 */
-        movl  %edx,%edx              /* Arg 3        */
-        movl  %edi,%r8d              /* Arg 5        */
-        movl  %ebp,%r9d              /* Arg 6        */
-        movl  UREGS_rbx(%rsp),%edi   /* Arg 1        */
-#define SHADOW_BYTES 0  /* No on-stack shadow state */
-#endif
-        cmpb  $0,tb_init_done(%rip)
-UNLIKELY_START(ne, compat_trace)
-        call  __trace_hypercall_entry
-        /* Restore the registers that __trace_hypercall_entry clobbered. */
-        movl  UREGS_rax+SHADOW_BYTES(%rsp),%eax   /* Hypercall #  */
-        movl  UREGS_rbx+SHADOW_BYTES(%rsp),%edi   /* Arg 1        */
-        movl  UREGS_rcx+SHADOW_BYTES(%rsp),%esi   /* Arg 2        */
-        movl  UREGS_rdx+SHADOW_BYTES(%rsp),%edx   /* Arg 3        */
-        movl  UREGS_rsi+SHADOW_BYTES(%rsp),%ecx   /* Arg 4        */
-        movl  UREGS_rdi+SHADOW_BYTES(%rsp),%r8d   /* Arg 5        */
-        movl  UREGS_rbp+SHADOW_BYTES(%rsp),%r9d   /* Arg 6        */
-#undef SHADOW_BYTES
-UNLIKELY_END(compat_trace)
-        leaq  compat_hypercall_table(%rip),%r10
-        PERFC_INCR(hypercalls, %rax, %rbx)
-        callq *(%r10,%rax,8)
-#ifndef NDEBUG
-        /* Deliberately corrupt parameter regs used by this hypercall. */
-        popq  %r10         # Shadow RIP
-        cmpq  %r10,UREGS_rip+8(%rsp)
-        popq  %rcx         # Shadow hypercall index
-        jne   compat_skip_clobber /* If RIP has changed then don't clobber. */
-        leaq  compat_hypercall_args_table(%rip),%r10
-        movb  (%r10,%rcx,1),%cl
-        movl  $0xDEADBEEF,%r10d
-        testb %cl,%cl; jz compat_skip_clobber; movl %r10d,UREGS_rbx(%rsp)
-        cmpb  $2, %cl; jb compat_skip_clobber; movl %r10d,UREGS_rcx(%rsp)
-        cmpb  $3, %cl; jb compat_skip_clobber; movl %r10d,UREGS_rdx(%rsp)
-        cmpb  $4, %cl; jb compat_skip_clobber; movl %r10d,UREGS_rsi(%rsp)
-        cmpb  $5, %cl; jb compat_skip_clobber; movl %r10d,UREGS_rdi(%rsp)
-        cmpb  $6, %cl; jb compat_skip_clobber; movl %r10d,UREGS_rbp(%rsp)
-compat_skip_clobber:
-#endif
+        mov   %rsp, %rdi
+        call  pv_hypercall
         movl  %eax,UREGS_rax(%rsp)       # save the return value
 
 /* %rbx: struct vcpu */
@@ -167,10 +107,6 @@ compat_process_trap:
         call  compat_create_bounce_frame
         jmp   compat_test_all_events
 
-compat_bad_hypercall:
-        movl $-ENOSYS,UREGS_rax(%rsp)
-        jmp  compat_test_all_events
-
 /* %rbx: struct vcpu, interrupts disabled */
 ENTRY(compat_restore_all_guest)
         ASSERT_INTERRUPTS_DISABLED
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index 5c6606b..1a7f8b7 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -101,60 +101,8 @@ ENTRY(lstar_enter)
         testb $TF_kernel_mode,VCPU_thread_flags(%rbx)
         jz    switch_to_kernel
 
-/*hypercall:*/
-        movq  %r10,%rcx
-        cmpq  $NR_hypercalls,%rax
-        jae   bad_hypercall
-#ifndef NDEBUG
-        /* Deliberately corrupt parameter regs not used by this hypercall. */
-        pushq %rdi; pushq %rsi; pushq %rdx; pushq %rcx; pushq %r8 ; pushq %r9 
-        leaq  hypercall_args_table(%rip),%r10
-        movq  $6,%rcx
-        sub   (%r10,%rax,1),%cl
-        movq  %rsp,%rdi
-        movl  $0xDEADBEEF,%eax
-        rep   stosq
-        popq  %r9 ; popq  %r8 ; popq  %rcx; popq  %rdx; popq  %rsi; popq  %rdi
-        movq  UREGS_rax(%rsp),%rax
-        pushq %rax
-        pushq UREGS_rip+8(%rsp)
-#define SHADOW_BYTES 16 /* Shadow EIP + shadow hypercall # */
-#else
-#define SHADOW_BYTES 0  /* No on-stack shadow state */
-#endif
-        cmpb  $0,tb_init_done(%rip)
-UNLIKELY_START(ne, trace)
-        call  __trace_hypercall_entry
-        /* Restore the registers that __trace_hypercall_entry clobbered. */
-        movq  UREGS_rax+SHADOW_BYTES(%rsp),%rax   /* Hypercall #  */
-        movq  UREGS_rdi+SHADOW_BYTES(%rsp),%rdi   /* Arg 1        */
-        movq  UREGS_rsi+SHADOW_BYTES(%rsp),%rsi   /* Arg 2        */
-        movq  UREGS_rdx+SHADOW_BYTES(%rsp),%rdx   /* Arg 3        */
-        movq  UREGS_r10+SHADOW_BYTES(%rsp),%rcx   /* Arg 4        */
-        movq  UREGS_r8 +SHADOW_BYTES(%rsp),%r8    /* Arg 5        */
-        movq  UREGS_r9 +SHADOW_BYTES(%rsp),%r9    /* Arg 6        */
-#undef SHADOW_BYTES
-UNLIKELY_END(trace)
-        leaq  hypercall_table(%rip),%r10
-        PERFC_INCR(hypercalls, %rax, %rbx)
-        callq *(%r10,%rax,8)
-#ifndef NDEBUG
-        /* Deliberately corrupt parameter regs used by this hypercall. */
-        popq  %r10         # Shadow RIP
-        cmpq  %r10,UREGS_rip+8(%rsp)
-        popq  %rcx         # Shadow hypercall index
-        jne   skip_clobber /* If RIP has changed then don't clobber. */
-        leaq  hypercall_args_table(%rip),%r10
-        movb  (%r10,%rcx,1),%cl
-        movl  $0xDEADBEEF,%r10d
-        cmpb  $1,%cl; jb skip_clobber; movq %r10,UREGS_rdi(%rsp)
-        cmpb  $2,%cl; jb skip_clobber; movq %r10,UREGS_rsi(%rsp)
-        cmpb  $3,%cl; jb skip_clobber; movq %r10,UREGS_rdx(%rsp)
-        cmpb  $4,%cl; jb skip_clobber; movq %r10,UREGS_r10(%rsp)
-        cmpb  $5,%cl; jb skip_clobber; movq %r10,UREGS_r8(%rsp)
-        cmpb  $6,%cl; jb skip_clobber; movq %r10,UREGS_r9(%rsp)
-skip_clobber:
-#endif
+        mov   %rsp, %rdi
+        call  pv_hypercall
         movq  %rax,UREGS_rax(%rsp)       # save the return value
 
 /* %rbx: struct vcpu */
@@ -231,10 +179,6 @@ process_trap:
         call create_bounce_frame
         jmp  test_all_events
 
-bad_hypercall:
-        movq $-ENOSYS,UREGS_rax(%rsp)
-        jmp  test_all_events
-
 ENTRY(sysenter_entry)
         sti
         pushq $FLAT_USER_SS
-- 
2.1.4


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