On Thu, Nov 2, 2023 at 2:41 PM Sean Christopherson [off-list ref] wrote:

On Thu, Nov 02, 2023, Fuad Tabba wrote:

quoted

Hi,

On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson [off-list ref] wrote:

quoted

Add flags to "struct kvm_gfn_range" to let notifier events target only
shared and only private mappings, and write up the existing mmu_notifier
events to be shared-only (private memory is never associated with a
userspace virtual address, i.e. can't be reached via mmu_notifiers).

Add two flags so that KVM can handle the three possibilities (shared,
private, and shared+private) without needing something like a tri-state
enum.

Link: https://lore.kernel.org/all/ZJX0hk+KpQP0KUyB@google.com (local)
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 include/linux/kvm_host.h | 2 ++
 virt/kvm/kvm_main.c      | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 96aa930536b1..89c1a991a3b8 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h

@@ -263,6 +263,8 @@ struct kvm_gfn_range {
        gfn_t start;
        gfn_t end;
        union kvm_mmu_notifier_arg arg;
+       bool only_private;
+       bool only_shared;

If these flags aren't used in this patch series, should this patch be
moved to the other series?

If *both* TDX and SNP need this patch, then I think it's probably worth applying
it now to make their lives easier.  But if only one needs the support, then I
completely agree this should be punted to whichever series needs it (this also
came up in v11, but we didn't force the issue).

Mike, Isaku?

quoted

Also, if shared+private is a possibility, doesn't the prefix "only_"
confuse things a bit? I.e., what is shared+private, is it when both
are 0 or when both are 1? I assume it's the former (both are 0), but
it might be clearer.

Heh, I was hoping that "only_private && only_shared" would be obviously nonsensical.

The only alternative I can think would be to add an enum, e.g.

        enum {
                PROCESS_PRIVATE_AND_SHARED,
                PROCESS_ONLY_PRIVATE,
                PROCESS_ONLY_SHARED,
        };

because every other way of expressing the flags either results in more confusion
or an unsafe default.  I.e. I want zapping only private or only shared to require
the caller to explicitly set a non-zero value, which is how I ended up with
"only_{private,shared}" as opposed to "process_{private,shared}".

I don't have a strong opinion about this. Having an enum looks good to me.

Cheers,
/fuad