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Date:   Tue, 06 Jun 2023 19:14:51 +0000
In-Reply-To: <ZEM5Zq8oo+xnApW9@google.com> (message from Sean Christopherson
 on Fri, 21 Apr 2023 18:33:26 -0700)
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Message-ID: <diqz8rcwjtck.fsf@ackerleytng-ctop.c.googlers.com>
Subject: Re: Rename restrictedmem => guardedmem? (was: Re: [PATCH v10 0/9]
 KVM: mm: fd-based approach for supporting KVM)
From:   Ackerley Tng <ackerleytng@google.com>
To:     Sean Christopherson <seanjc@google.com>
Cc:     david@redhat.com, chao.p.peng@linux.intel.com, pbonzini@redhat.com,
        vkuznets@redhat.com, jmattson@google.com, joro@8bytes.org,
        mail@maciej.szmigiero.name, vbabka@suse.cz, vannapurve@google.com,
        yu.c.zhang@linux.intel.com, kirill.shutemov@linux.intel.com,
        dhildenb@redhat.com, qperret@google.com, tabba@google.com,
        michael.roth@amd.com, wei.w.wang@intel.com, rppt@kernel.org,
        liam.merwick@oracle.com, isaku.yamahata@gmail.com,
        jarkko@kernel.org, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, hughd@google.com, brauner@kernel.org
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I've ported selftests from Chao and I [1] while working on hugetlb support  
for
guest_mem [2].

In the process, I found some bugs and have some suggestions for guest_mem.
Please see separate commits at [3].

Here are some highlights/questions:

+ "KVM: guest_mem: Explain the use of the uptodate flag for gmem"
     + Generally, uptodate flags means that the contents of this page match  
the
       backing store. Since gmem is memory-backed, does "uptodate" for gmem  
mean
       "zeroed"?
+ "KVM: guest_mem: Don't re-mark accessed after getting a folio" and "KVM:
   guest_mem: Don't set dirty flag for folio"
     + Do we need to folio_mark_accessed(), when it was created with
       FGP_ACCESSED?
     + What is the significance of these LRU flags when gmem doesn't support
       swapping/eviction?
+ "KVM: guest_mem: Align so that at least 1 page is allocated"
     + Bug in current implementation: without this alignment, fallocate() of  
a
       size less than the gmem page size will result in no allocation at all
     + Both shmem and hugetlbfs perform this alignment
+ "KVM: guest_mem: Add alignment checks"
     + Implemented the alignment checks for guest_mem because hugetlb on gmem
       would hit a BUG_ON without this check
+ "KVM: guest_mem: Prevent overflows in kvm_gmem_invalidate_begin()"
     + Sean fixed a bug in the offset-to-gfn conversion in
       kvm_gmem_invalidate_begin() earlier, adding a WARN_ON_ONCE()
     + Code will always hit WARN_ON_ONCE() when the entire file is closed  
and all
       offsets are invalidated, so WARN_ON_ONCE() should be removed
     + Vishal noticed that the conversion might result in an overflow, so I  
fixed
       that
+ And of course, hugetlb support! Please let me know what you think of the
   approach proposed at [2].

[1]  
https://lore.kernel.org/all/cover.1678926164.git.ackerleytng@google.com/T/
[2]  
https://lore.kernel.org/lkml/cover.1686077275.git.ackerleytng@google.com/T/
[3] https://github.com/googleprodkernel/linux-cc/tree/gmem-hugetlb-rfc-v1