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Re: [RFC-for-4.20 v2 0/1] x86/hvm: Introduce Xen-wide ASID allocator
Hi All,
Gentle ping, I would appreciate some reviews here. Especially because in v2
the whole domain liefcylce with the fixed ASID works. So, I would love to
know if it's going in the right direction or not.
Thanks!
On 8/13/24 8:58 PM, Vaishali Thakkar wrote:
Motivation:
-----------
This is part of the effort to enable AMD SEV technologies in Xen. For
AMD SEV support, we need a fixed ASID associated with all vcpus of the
same domain throughout the domain's lifetime. This is because for SEV/
SEV-{ES,SNP} VM, the ASID is the index which is associated with the
encryption key.
Currently, ASID generation and management is done per-PCPU in Xen. And
at the time of each VMENTER, the ASID associated with vcpus of the
domain is changed. This implementation is incompatible with SEV
technologies for the above mentioned reasons. In a discussion with
Andrew Cooper, it came up that it’ll be nice to have fixed ASIDs not
only for SEV VMs but also for all VMs. Because it opens up the
opportunity to use instructions like TLBSYNC and INVLPGB (Section
5.5.3 in AMD Architecture manual[0]) for broadcasting the TLB
Invalidations.
Changes since v1:
-----------------
As discussed in v1 and at the Xen summit, this version changes the
flow of the asid assignment. I initialize asids by calling CPUID
on each cpu during the __start_xen. The assignment of the asid
happens at the domain creation time at HVM level and later it is
mapped to individual hardware fields ASID/VPID at the VMRUN. ASID
is flushed when the domain is destroyed. Please check the comment in
xen/arch/x86/hvm/asid.c to check the implemenmtation flow. Detailed
list of changes is mentioned in the patch.
Few questions I have:
---------------------
1. While in this version I keep using hvm_asid_flush_domain in svm_invlpg,
I'm wondering if we need to do hvm_asid_flush_vcpu in this case? If so,
what would be the preferred way to flush vcpu specific TLB entries here?
2. Currently I assign asid at the VCPU level at VMRUN. But is there any
way to do it more early in the process? I tried to do it after the
hvm_vcpu_initialize and hvm_vcpu_up but wasn't really successfull in
doing so.
3. While there is a plan to use TLBSYNC in the future. My understanding
is intel doesn't have an equivalent instruction. Do we need a separate
function that is able to do it?
4. How is the freeing of resources done when Xen is destroyed? I couldn't
find something equivalent of svm_hardware_unsetup in linux kernel.
Notes:
------
1. As discussed at Xen Summit, changes related to demonstrating the use
of TLBSYNC and INVLPGB won't be part of this patchset.
2. Changes are tested on AMD EPYC Genoa at the moment.
Vaishali Thakkar (1):
x86/hvm: Introduce Xen-wide ASID allocator
xen/arch/x86/domain.c | 7 ++
xen/arch/x86/flushtlb.c | 4 -
xen/arch/x86/hvm/asid.c | 136 +++++++++++++------------
xen/arch/x86/hvm/hvm.c | 6 +-
xen/arch/x86/hvm/nestedhvm.c | 4 +-
xen/arch/x86/hvm/svm/asid.c | 37 ++++---
xen/arch/x86/hvm/svm/nestedsvm.c | 5 +-
xen/arch/x86/hvm/svm/svm.c | 32 ++----
xen/arch/x86/hvm/svm/svm.h | 3 -
xen/arch/x86/hvm/vmx/vmcs.c | 2 -
xen/arch/x86/hvm/vmx/vmx.c | 37 ++-----
xen/arch/x86/hvm/vmx/vvmx.c | 7 +-
xen/arch/x86/include/asm/hvm/asid.h | 24 ++---
xen/arch/x86/include/asm/hvm/domain.h | 7 ++
xen/arch/x86/include/asm/hvm/hvm.h | 11 --
xen/arch/x86/include/asm/hvm/svm/svm.h | 2 +
xen/arch/x86/include/asm/hvm/vcpu.h | 9 --
xen/arch/x86/include/asm/hvm/vmx/vmx.h | 3 +-
xen/arch/x86/mm/hap/hap.c | 5 +-
xen/arch/x86/mm/p2m.c | 6 +-
xen/arch/x86/mm/paging.c | 3 +-
xen/arch/x86/pv/domain.c | 1 +
xen/arch/x86/setup.c | 10 ++
23 files changed, 173 insertions(+), 188 deletions(-)
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