[xen stable-4.13] x86/spec-ctrl: Drop SPEC_CTRL_{ENTRY_FROM,EXIT_TO}_HVM

[patchbot@xxxxxxx]

commit 8a2cc1ed1aee291de3c06fae90763bd79248b043
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Tue Jan 25 13:52:56 2022 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Tue Jul 12 16:33:19 2022 +0100

    x86/spec-ctrl: Drop SPEC_CTRL_{ENTRY_FROM,EXIT_TO}_HVM
    
    These were written before Spectre/Meltdown went public, and there was large
    uncertainty in how the protections would evolve.  As it turns out, they're
    very specific to Intel hardware, and not very suitable for AMD.
    
    Drop the macros, opencoding the relevant subset of functionality, and 
leaving
    grep-fodder to locate the logic.  No change at all for VT-x.
    
    For AMD, the only relevant piece of functionality is DO_OVERWRITE_RSB,
    although we will soon be adding (different) logic to handle MSR_SPEC_CTRL.
    
    This has a marginal improvement of removing an unconditional pile of 
long-nops
    from the vmentry/exit path.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    (cherry picked from commit 95b13fa43e0753b7514bef13abe28253e8614f62)
    [Forward port over XSA-404]
---
 xen/arch/x86/hvm/svm/entry.S        |  5 +++--
 xen/arch/x86/hvm/vmx/entry.S        |  7 +++++--
 xen/include/asm-x86/spec_ctrl_asm.h | 17 ++++-------------
 3 files changed, 12 insertions(+), 17 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/entry.S b/xen/arch/x86/hvm/svm/entry.S
index e954d8e021..0684d29050 100644
--- a/xen/arch/x86/hvm/svm/entry.S
+++ b/xen/arch/x86/hvm/svm/entry.S
@@ -63,7 +63,7 @@ __UNLIKELY_END(nsvm_hap)
         mov VCPUMSR_spec_ctrl_raw(%rax), %eax
 
         /* WARNING! `ret`, `call *`, `jmp *` not safe beyond this point. */
-        SPEC_CTRL_EXIT_TO_HVM   /* Req: a=spec_ctrl %rsp=regs/cpuinfo, Clob: 
cd */
+        /* SPEC_CTRL_EXIT_TO_SVM   (nothing currently) */
 
         pop  %r15
         pop  %r14
@@ -90,7 +90,8 @@ __UNLIKELY_END(nsvm_hap)
 
         GET_CURRENT(bx)
 
-        SPEC_CTRL_ENTRY_FROM_HVM    /* Req: b=curr %rsp=regs/cpuinfo, Clob: 
acd */
+        /* SPEC_CTRL_ENTRY_FROM_SVM    Req: b=curr %rsp=regs/cpuinfo, Clob: ac 
 */
+        ALTERNATIVE "", DO_OVERWRITE_RSB, X86_FEATURE_SC_RSB_HVM
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
         STGI
diff --git a/xen/arch/x86/hvm/vmx/entry.S b/xen/arch/x86/hvm/vmx/entry.S
index 62ed0d854d..db3af571c9 100644
--- a/xen/arch/x86/hvm/vmx/entry.S
+++ b/xen/arch/x86/hvm/vmx/entry.S
@@ -33,7 +33,9 @@ ENTRY(vmx_asm_vmexit_handler)
         movb $1,VCPU_vmx_launched(%rbx)
         mov  %rax,VCPU_hvm_guest_cr2(%rbx)
 
-        SPEC_CTRL_ENTRY_FROM_HVM    /* Req: b=curr %rsp=regs/cpuinfo, Clob: 
acd */
+        /* SPEC_CTRL_ENTRY_FROM_VMX    Req: b=curr %rsp=regs/cpuinfo, Clob: 
acd */
+        ALTERNATIVE "", DO_OVERWRITE_RSB, X86_FEATURE_SC_RSB_HVM
+        ALTERNATIVE "", DO_SPEC_CTRL_ENTRY_FROM_HVM, X86_FEATURE_SC_MSR_HVM
         /* WARNING! `ret`, `call *`, `jmp *` not safe before this point. */
 
         /* Hardware clears MSR_DEBUGCTL on VMExit.  Reinstate it if debugging 
Xen. */
@@ -80,7 +82,8 @@ UNLIKELY_END(realmode)
         mov VCPUMSR_spec_ctrl_raw(%rax), %eax
 
         /* WARNING! `ret`, `call *`, `jmp *` not safe beyond this point. */
-        SPEC_CTRL_EXIT_TO_HVM   /* Req: a=spec_ctrl %rsp=regs/cpuinfo, Clob: 
cd */
+        /* SPEC_CTRL_EXIT_TO_VMX   Req: a=spec_ctrl %rsp=regs/cpuinfo, Clob: 
cd */
+        ALTERNATIVE "", DO_SPEC_CTRL_EXIT_TO_GUEST, X86_FEATURE_SC_MSR_HVM
         DO_SPEC_CTRL_COND_VERW
 
         mov  VCPU_hvm_guest_cr2(%rbx),%rax
diff --git a/xen/include/asm-x86/spec_ctrl_asm.h 
b/xen/include/asm-x86/spec_ctrl_asm.h
index 4a3777cc52..fe90c80ac3 100644
--- a/xen/include/asm-x86/spec_ctrl_asm.h
+++ b/xen/include/asm-x86/spec_ctrl_asm.h
@@ -68,14 +68,16 @@
  *
  * The following ASM fragments implement this algorithm.  See their local
  * comments for further details.
- *  - SPEC_CTRL_ENTRY_FROM_HVM
  *  - SPEC_CTRL_ENTRY_FROM_PV
  *  - SPEC_CTRL_ENTRY_FROM_INTR
  *  - SPEC_CTRL_ENTRY_FROM_INTR_IST
  *  - SPEC_CTRL_EXIT_TO_XEN_IST
  *  - SPEC_CTRL_EXIT_TO_XEN
  *  - SPEC_CTRL_EXIT_TO_PV
- *  - SPEC_CTRL_EXIT_TO_HVM
+ *
+ * Additionally, the following grep-fodder exists to find the HVM logic.
+ *  - SPEC_CTRL_ENTRY_FROM_{SVM,VMX}
+ *  - SPEC_CTRL_EXIT_TO_{SVM,VMX}
  */
 
 .macro DO_OVERWRITE_RSB tmp=rax
@@ -228,12 +230,6 @@
     wrmsr
 .endm
 
-/* Use after a VMEXIT from an HVM guest. */
-#define SPEC_CTRL_ENTRY_FROM_HVM                                        \
-    ALTERNATIVE "", DO_OVERWRITE_RSB, X86_FEATURE_SC_RSB_HVM;           \
-    ALTERNATIVE "", DO_SPEC_CTRL_ENTRY_FROM_HVM,                        \
-        X86_FEATURE_SC_MSR_HVM
-
 /* Use after an entry from PV context (syscall/sysenter/int80/int82/etc). */
 #define SPEC_CTRL_ENTRY_FROM_PV                                         \
     ALTERNATIVE "", DO_OVERWRITE_RSB, X86_FEATURE_SC_RSB_PV;            \
@@ -257,11 +253,6 @@
         DO_SPEC_CTRL_EXIT_TO_GUEST, X86_FEATURE_SC_MSR_PV;              \
     DO_SPEC_CTRL_COND_VERW
 
-/* Use when exiting to HVM guest context. */
-#define SPEC_CTRL_EXIT_TO_HVM                                           \
-    ALTERNATIVE "",                                                     \
-        DO_SPEC_CTRL_EXIT_TO_GUEST, X86_FEATURE_SC_MSR_HVM;             \
-
 /*
  * Use in IST interrupt/exception context.  May interrupt Xen or PV context.
  * Fine grain control of SCF_ist_wrmsr is needed for safety in the S3 resume
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.13