Re: SEV guest debugging support for Qemu

[Paolo Bonzini <pbonzini@redhat.com>]

On 22/09/20 22:11, Ashish Kalra wrote:
> This internally invokes the address_space_rw() accessor functions
> which we had  "fixed" internally (as part of the earlier patch) to
> invoke memory region specific debug ops. In our earlier approach we
> were adding debug ops/callbacks to memory regions and as per comments
> on our earlier patches, Paolo was not happy with this debug API for 
> MemoryRegions and hence the SEV support for Qemu was merged without
> the debug support.

My complaint was only about hooking into address_space_read and
address_space_write; I think the hook should not touch general-purpose
(non-debug) code if possible, so something like this:

typedef struct MemoryDebugOps {
    hwaddr (*translate)(CPUState *cpu, target_ulong addr,
                        MemTxAttrs *attrs);
    MemTxResult (*read)(AddressSpace *as, hwaddr phys_addr,
                        MemTxAttrs attrs, void *buf,
                        hwaddr len);
    MemTxResult (*write)(AddressSpace *as, hwaddr phys_addr,
                         MemTxAttrs attrs, const void *buf,
                         hwaddr len);
} MemoryDebugOps;

These ops would be used only by cpu_memory_rw_debug and would default to

static const MemoryDebugOps default_debug_ops = {
    .translate = cpu_get_phys_page_attrs_debug,
    .read = address_space_read,
    .write = address_space_write_rom
};

static const MemoryDebugOps *debug_ops = &default_debug_ops;

Paolo