KVM: PPC: Book3S 64: Minimise hcall handler calling convention differences

This sets up the same calling convention from interrupt entry to
KVM interrupt handler for system calls as exists for other interrupt
types.

This is a better API, it uses a save area rather than SPR, and it has
more registers free to use. Using a single common API helps maintain
it, and it becomes easier to use in C in a later patch.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210528090752.3542186-8-npiggin@gmail.com

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index bf377bfeeb1a4b82034f97614baf7d22cc47c65e..f7fc6e078d4edbc6c97df76830c7e459e6e10588 100644 (file)
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -1869,8 +1869,27 @@ EXC_VIRT_END(system_call, 0x4c00, 0x100)
 
 #ifdef CONFIG_KVM_BOOK3S_64_HANDLER
 TRAMP_REAL_BEGIN(kvm_hcall)
+       std     r9,PACA_EXGEN+EX_R9(r13)
+       std     r11,PACA_EXGEN+EX_R11(r13)
+       std     r12,PACA_EXGEN+EX_R12(r13)
+       mfcr    r9
        mfctr   r10
-       SET_SCRATCH0(r10) /* Save r13 in SCRATCH0 */
+       std     r10,PACA_EXGEN+EX_R13(r13)
+       li      r10,0
+       std     r10,PACA_EXGEN+EX_CFAR(r13)
+       std     r10,PACA_EXGEN+EX_CTR(r13)
+        /*
+         * Save the PPR (on systems that support it) before changing to
+         * HMT_MEDIUM. That allows the KVM code to save that value into the
+         * guest state (it is the guest's PPR value).
+         */
+BEGIN_FTR_SECTION
+       mfspr   r10,SPRN_PPR
+       std     r10,PACA_EXGEN+EX_PPR(r13)
+END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
+
+       HMT_MEDIUM
+
 #ifdef CONFIG_RELOCATABLE
        /*
         * Requires __LOAD_FAR_HANDLER beause kvmppc_hcall lives

diff --git a/arch/powerpc/kvm/book3s_64_entry.S b/arch/powerpc/kvm/book3s_64_entry.S
index 66170ea85bc2a7ee157a94b2ee95bbd6a7a70aa2..a01046202eef4c512d6e4d26a601549dd457cf58 100644 (file)
--- a/arch/powerpc/kvm/book3s_64_entry.S
+++ b/arch/powerpc/kvm/book3s_64_entry.S
@@ -11,40 +11,30 @@
  * These are branched to from interrupt handlers in exception-64s.S which set
  * IKVM_REAL or IKVM_VIRT, if HSTATE_IN_GUEST was found to be non-zero.
  */
+
+/*
+ * This is a hcall, so register convention is as
+ * Documentation/powerpc/papr_hcalls.rst.
+ *
+ * This may also be a syscall from PR-KVM userspace that is to be
+ * reflected to the PR guest kernel, so registers may be set up for
+ * a system call rather than hcall. We don't currently clobber
+ * anything here, but the 0xc00 handler has already clobbered CTR
+ * and CR0, so PR-KVM can not support a guest kernel that preserves
+ * those registers across its system calls.
+ *
+ * The state of registers is as kvmppc_interrupt, except CFAR is not
+ * saved, R13 is not in SCRATCH0, and R10 does not contain the trap.
+ */
 .global        kvmppc_hcall
 .balign IFETCH_ALIGN_BYTES
 kvmppc_hcall:
-       /*
-        * This is a hcall, so register convention is as
-        * Documentation/powerpc/papr_hcalls.rst, with these additions:
-        * R13          = PACA
-        * guest R13 saved in SPRN_SCRATCH0
-        * R10          = free
-        * guest r10 saved in PACA_EXGEN
-        *
-        * This may also be a syscall from PR-KVM userspace that is to be
-        * reflected to the PR guest kernel, so registers may be set up for
-        * a system call rather than hcall. We don't currently clobber
-        * anything here, but the 0xc00 handler has already clobbered CTR
-        * and CR0, so PR-KVM can not support a guest kernel that preserves
-        * those registers across its system calls.
-        */
-        /*
-         * Save the PPR (on systems that support it) before changing to
-         * HMT_MEDIUM. That allows the KVM code to save that value into the
-         * guest state (it is the guest's PPR value).
-         */
-BEGIN_FTR_SECTION
-       mfspr   r10,SPRN_PPR
-       std     r10,HSTATE_PPR(r13)
-END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
-       HMT_MEDIUM
-       mfcr    r10
-       std     r12,HSTATE_SCRATCH0(r13)
-       sldi    r12,r10,32
-       ori     r12,r12,0xc00
-       ld      r10,PACA_EXGEN+EX_R10(r13)
-       b       do_kvm_interrupt
+       ld      r10,PACA_EXGEN+EX_R13(r13)
+       SET_SCRATCH0(r10)
+       li      r10,0xc00
+       /* Now we look like kvmppc_interrupt */
+       li      r11,PACA_EXGEN
+       b       .Lgot_save_area
 
 /*
  * KVM interrupt entry occurs after GEN_INT_ENTRY runs, and follows that
@@ -67,12 +57,12 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 kvmppc_interrupt:
        li      r11,PACA_EXGEN
        cmpdi   r10,0x200
-       bgt+    1f
+       bgt+    .Lgot_save_area
        li      r11,PACA_EXMC
-       beq     1f
+       beq     .Lgot_save_area
        li      r11,PACA_EXNMI
-1:     add     r11,r11,r13
-
+.Lgot_save_area:
+       add     r11,r11,r13
 BEGIN_FTR_SECTION
        ld      r12,EX_CFAR(r11)
        std     r12,HSTATE_CFAR(r13)
@@ -91,7 +81,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
        ld      r10,EX_R10(r11)
        ld      r11,EX_R11(r11)
 
-do_kvm_interrupt:
        /*
         * Hcalls and other interrupts come here after normalising register
         * contents and save locations: