On 3/29/22 17:36, Lai Jiangshan wrote:
From: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
(Request For Help for testing on AMD machine with 32 bit L1 hypervisor,
see information below)
KVM handles root pages specially for these cases:
direct mmu (nonpaping for 32 bit guest):
gCR0_PG=0
shadow mmu (shadow paping for 32 bit guest):
gCR0_PG=1,gEFER_LMA=0,gCR4_PSE=0
gCR0_PG=1,gEFER_LMA=0,gCR4_PSE=1
direct mmu (NPT for 32bit host):
hEFER_LMA=0
shadow nested NPT (for 32bit L1 hypervisor):
gCR0_PG=1,gEFER_LMA=0,gCR4_PSE=0,hEFER_LMA=0
gCR0_PG=1,gEFER_LMA=0,gCR4_PSE=1,hEFER_LMA=0
gCR0_PG=1,gEFER_LMA=0,gCR4_PSE={0|1},hEFER_LMA=1,hCR4_LA57={0|1}
Shadow nested NPT for 64bit L1 hypervisor:
gEFER_LMA=1,gCR4_LA57=0,hEFER_LMA=1,hCR4_LA57=1
They are either using special roots or matched the condition
((mmu->shadow_root_level > mmu->root_level) && !mm->direct_map)
(refered as level expansion) or both.
All the cases are using special roots except the last one.
Many cases are doing level expansion including the last one.
Hi Jiangshan,
so the main difference between direct and passthrough shadow pages is
that passthrough pages can have indirect children. A direct page maps
the page at sp->gfn, while a passthrough page maps the page _table_ at
sp->gfn. Is this correct?
If so, I think there is a difference between a passthrough page that
maps a level-2 page from level-4, and a passthrough page that maps a
level-3 page from level-4. If that is true, a single bit in the role
is not enough.
One way to handle this could be to have a single field "mapping_level"
that subsumes both "direct" and "passthrough". direct==1
would correspond to "mapping_level == 0"; direct==0 && passthrough==0
would be "mapping_level == level"; anything in the middle would be a
passthrough page in your series.
What do you think?
Thanks,
Paolo
