Commit b8892129 authored by Liran Alon's avatar Liran Alon Committed by Paolo Bonzini
Browse files

hw/i386/vmport: Propagate IOPort read to vCPU EAX register 



vmport_ioport_read() returns the value that should propagate to vCPU EAX
register when guest reads VMPort IOPort (i.e. By x86 IN instruction).

However, because vmport_ioport_read() calls cpu_synchronize_state(), the
returned value gets overridden by the value in QEMU vCPU EAX register.
i.e. cpu->env.regs[R_EAX].

To fix this issue, change vmport_ioport_read() to explicitly override
cpu->env.regs[R_EAX] with the value it wish to propagate to vCPU EAX
register.

Reviewed-by: default avatarNikita Leshenko <nikita.leshchenko@oracle.com>
Signed-off-by: default avatarLiran Alon <liran.alon@oracle.com>
Message-Id: <20200312165431.82118-4-liran.alon@oracle.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent c9ab24ce

hw/core/machine.c

+1 −0
Original line number Diff line number Diff line
@@ -43,6 +43,7 @@ GlobalProperty hw_compat_4_2[] = { 
    { "qxl", "revision", "4" },

    { "qxl-vga", "revision", "4" },

    { "fw_cfg", "acpi-mr-restore", "false" },

    { "vmport", "x-read-set-eax", "off" },

};

const size_t hw_compat_4_2_len = G_N_ELEMENTS(hw_compat_4_2);

hw/i386/vmport.c

+29 −3
Original line number Diff line number Diff line
@@ -43,6 +43,11 @@ 
#define VMPORT_ENTRIES 0x2c

#define VMPORT_MAGIC   0x564D5868



/* Compatibility flags for migration */

#define VMPORT_COMPAT_READ_SET_EAX_BIT      0

#define VMPORT_COMPAT_READ_SET_EAX          \

    (1 << VMPORT_COMPAT_READ_SET_EAX_BIT)



#define VMPORT(obj) OBJECT_CHECK(VMPortState, (obj), TYPE_VMPORT)



typedef struct VMPortState {
@@ -51,6 +56,8 @@ typedef struct VMPortState { 
    MemoryRegion io;

    VMPortReadFunc *func[VMPORT_ENTRIES];

    void *opaque[VMPORT_ENTRIES];



    uint32_t compat_flags;

} VMPortState;



static VMPortState *port_state;
@@ -80,17 +87,33 @@ static uint64_t vmport_ioport_read(void *opaque, hwaddr addr, 


    eax = env->regs[R_EAX];

    if (eax != VMPORT_MAGIC) {

        return eax;

        goto out;

    }



    command = env->regs[R_ECX];

    trace_vmport_command(command);

    if (command >= VMPORT_ENTRIES || !s->func[command]) {

        qemu_log_mask(LOG_UNIMP, "vmport: unknown command %x\n", command);

        return eax;

        goto out;

    }



    return s->func[command](s->opaque[command], addr);

    eax = s->func[command](s->opaque[command], addr);



out:

    /*

     * The call above to cpu_synchronize_state() gets vCPU registers values

     * to QEMU but also cause QEMU to write QEMU vCPU registers values to

     * vCPU implementation (e.g. Accelerator such as KVM) just before

     * resuming guest.

     *

     * Therefore, in order to make IOPort return value propagate to

     * guest EAX, we need to explicitly update QEMU EAX register value.

     */

    if (s->compat_flags & VMPORT_COMPAT_READ_SET_EAX) {

        cpu->env.regs[R_EAX] = eax;

    }



    return eax;

}



static void vmport_ioport_write(void *opaque, hwaddr addr,
@@ -142,6 +165,9 @@ static void vmport_realizefn(DeviceState *dev, Error **errp) 
}



static Property vmport_properties[] = {

    /* Used to enforce compatibility for migration */

    DEFINE_PROP_BIT("x-read-set-eax", VMPortState, compat_flags,

                    VMPORT_COMPAT_READ_SET_EAX_BIT, true),

    DEFINE_PROP_END_OF_LIST(),

};