[PATCH v6 12/16] x86/hvm: remove HVMIO_dispatched I/O state

[Paul Durrant <paul.durrant@citrix.com>]

By removing the HVMIO_dispatched state and making all pending emulations
(i.e. all those not handled by the hypervisor) use HVMIO_awating_completion,
various code-paths can be simplified.

The completion case for HVMIO_dispatched can also be trivally removed
from hvmemul_do_io() as it was already unreachable. This is because that
state was only ever used for writes or I/O to/from a guest page and
hvmemul_do_io() is never called to complete such I/O.

NOTE: There is one sublety in handle_pio()... The only case when
      handle_pio() got a return code of X86EMUL_RETRY back from
      hvmemul_do_pio_buffer() and found io_state was not
      HVMIO_awaiting_completion was in the case where the domain is
      shutting down. This is because all writes normally yield a return
      of HVMEMUL_OKAY and all reads put io_state into
      HVMIO_awaiting_completion. Hence the io_state check there is
      replaced with a check of the is_shutting_down flag on the domain.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Cc: Keir Fraser <keir@xen.org>
Cc: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
 xen/arch/x86/hvm/emulate.c      |   12 +++---------
 xen/arch/x86/hvm/hvm.c          |   12 +++---------
 xen/arch/x86/hvm/io.c           |   14 +++++++-------
 xen/arch/x86/hvm/vmx/realmode.c |    2 +-
 xen/include/asm-x86/hvm/vcpu.h  |   10 +++++++++-
 5 files changed, 23 insertions(+), 27 deletions(-)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index d1775ac..c694bb1 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -137,20 +137,14 @@ static int hvmemul_do_io(
         if ( data_is_addr || dir == IOREQ_WRITE )
             return X86EMUL_UNHANDLEABLE;
         goto finish_access;
-    case HVMIO_dispatched:
-        /* May have to wait for previous cycle of a multi-write to complete. */
-        if ( is_mmio && !data_is_addr && (dir == IOREQ_WRITE) &&
-             (addr == (vio->mmio_large_write_pa +
-                       vio->mmio_large_write_bytes)) )
-            return X86EMUL_RETRY;
-        /* fallthrough */
     default:
         return X86EMUL_UNHANDLEABLE;
     }
 
-    vio->io_state = (data_is_addr || dir == IOREQ_WRITE) ?
-        HVMIO_dispatched : HVMIO_awaiting_completion;
+    vio->io_state = HVMIO_awaiting_completion;
     vio->io_size = size;
+    vio->io_dir = dir;
+    vio->io_data_is_addr = data_is_addr;
 
     if ( dir == IOREQ_WRITE )
     {
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 98d1536..4aa7ed2 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -416,22 +416,16 @@ static void hvm_io_assist(ioreq_t *p)
 {
     struct vcpu *curr = current;
     struct hvm_vcpu_io *vio = &curr->arch.hvm_vcpu.hvm_io;
-    enum hvm_io_state io_state;
 
     p->state = STATE_IOREQ_NONE;
 
-    io_state = vio->io_state;
-    vio->io_state = HVMIO_none;
-
-    switch ( io_state )
+    if ( hvm_vcpu_io_need_completion(vio) )
     {
-    case HVMIO_awaiting_completion:
         vio->io_state = HVMIO_completed;
         vio->io_data = p->data;
-        break;
-    default:
-        break;
     }
+    else
+        vio->io_state = HVMIO_none;
 
     msix_write_completion(curr);
     vcpu_end_shutdown_deferral(curr);
diff --git a/xen/arch/x86/hvm/io.c b/xen/arch/x86/hvm/io.c
index 221d05e..3b51d59 100644
--- a/xen/arch/x86/hvm/io.c
+++ b/xen/arch/x86/hvm/io.c
@@ -90,9 +90,7 @@ int handle_mmio(void)
 
     rc = hvm_emulate_one(&ctxt);
 
-    if ( rc != X86EMUL_RETRY )
-        vio->io_state = HVMIO_none;
-    if ( vio->io_state == HVMIO_awaiting_completion || vio->mmio_retry )
+    if ( hvm_vcpu_io_need_completion(vio) || vio->mmio_retry )
         vio->io_completion = HVMIO_mmio_completion;
     else
         vio->mmio_access = (struct npfec){};
@@ -142,6 +140,9 @@ int handle_pio(uint16_t port, unsigned int size, int dir)
 
     rc = hvmemul_do_pio_buffer(port, size, dir, &data);
 
+    if ( hvm_vcpu_io_need_completion(vio) )
+        vio->io_completion = HVMIO_pio_completion;
+
     switch ( rc )
     {
     case X86EMUL_OKAY:
@@ -154,11 +155,10 @@ int handle_pio(uint16_t port, unsigned int size, int dir)
         }
         break;
     case X86EMUL_RETRY:
-        if ( vio->io_state != HVMIO_awaiting_completion )
+        /* We should not advance RIP/EIP if the domain is shutting down */
+        if ( curr->domain->is_shutting_down )
             return 0;
-        /* Completion in hvm_io_assist() with no re-emulation required. */
-        ASSERT(dir == IOREQ_READ);
-        vio->io_completion = HVMIO_pio_completion;
+
         break;
     default:
         gdprintk(XENLOG_ERR, "Weird HVM ioemulation status %d.\n", rc);
diff --git a/xen/arch/x86/hvm/vmx/realmode.c b/xen/arch/x86/hvm/vmx/realmode.c
index 76ff9a5..deb53ae 100644
--- a/xen/arch/x86/hvm/vmx/realmode.c
+++ b/xen/arch/x86/hvm/vmx/realmode.c
@@ -111,7 +111,7 @@ void vmx_realmode_emulate_one(struct hvm_emulate_ctxt *hvmemul_ctxt)
 
     rc = hvm_emulate_one(hvmemul_ctxt);
 
-    if ( vio->io_state == HVMIO_awaiting_completion || vio->mmio_retry )
+    if ( hvm_vcpu_io_need_completion(vio) || vio->mmio_retry )
         vio->io_completion = HVMIO_realmode_completion;
 
     if ( rc == X86EMUL_UNHANDLEABLE )
diff --git a/xen/include/asm-x86/hvm/vcpu.h b/xen/include/asm-x86/hvm/vcpu.h
index dbdee14..de8cdd7 100644
--- a/xen/include/asm-x86/hvm/vcpu.h
+++ b/xen/include/asm-x86/hvm/vcpu.h
@@ -32,7 +32,6 @@
 
 enum hvm_io_state {
     HVMIO_none = 0,
-    HVMIO_dispatched,
     HVMIO_awaiting_completion,
     HVMIO_completed
 };
@@ -55,6 +54,8 @@ struct hvm_vcpu_io {
     unsigned long          io_data;
     unsigned int           io_size;
     enum hvm_io_completion io_completion;
+    uint8_t                io_dir;
+    uint8_t                io_data_is_addr;
 
     /*
      * HVM emulation:
@@ -87,6 +88,13 @@ struct hvm_vcpu_io {
     const struct g2m_ioport *g2m_ioport;
 };
 
+static inline bool_t hvm_vcpu_io_need_completion(const struct hvm_vcpu_io *vio)
+{
+    return (vio->io_state == HVMIO_awaiting_completion) &&
+           !vio->io_data_is_addr &&
+           (vio->io_dir == IOREQ_READ);
+}
+
 #define VMCX_EADDR    (~0ULL)
 
 struct nestedvcpu {
-- 
1.7.10.4