[Xen-devel] Question about PV kernel ring

["Liu, Jinsong" <jinsong.liu@xxxxxxxxx>]

Keir,

I have a question about pv kernel ring arrangement:

arch/x86/x86_32/traps.c
void hypercall_page_initialise(struct domain *d, void *hypercall_page)
{
    memset(hypercall_page, 0xCC, PAGE_SIZE);
    if ( is_hvm_domain(d) )
        hvm_hypercall_page_initialise(d, hypercall_page);
    else if ( supervisor_mode_kernel )
        hypercall_page_initialise_ring0_kernel(hypercall_page);
    else
        hypercall_page_initialise_ring1_kernel(hypercall_page);
}

arch/x86/x86_64/traps.c
void hypercall_page_initialise(struct domain *d, void *hypercall_page)
{
    memset(hypercall_page, 0xCC, PAGE_SIZE);
    if ( is_hvm_domain(d) )
        hvm_hypercall_page_initialise(d, hypercall_page);
    else if ( !is_pv_32bit_domain(d) )
        hypercall_page_initialise_ring3_kernel(hypercall_page);
    else
        hypercall_page_initialise_ring1_kernel(hypercall_page);
}

My question:
1. for x86_32 hypervisor, what's the purpose and advantage/disadvantage of 
supervisor_mode_kernel pv which runs at ring0?
2. for x86_64 hypervisor, why no supervisor_mode_kernel pv? seems pv can also 
do so ...


Thanks,
Jinsong
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