linux-kernel - Re: Rename restrictedmem => guardedmem? (was: Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM)

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Date:   Tue, 06 Jun 2023 19:14:51 +0000
From:   Ackerley Tng <ackerleytng@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     david@...hat.com, chao.p.peng@...ux.intel.com, pbonzini@...hat.com,
        vkuznets@...hat.com, jmattson@...gle.com, joro@...tes.org,
        mail@...iej.szmigiero.name, vbabka@...e.cz, vannapurve@...gle.com,
        yu.c.zhang@...ux.intel.com, kirill.shutemov@...ux.intel.com,
        dhildenb@...hat.com, qperret@...gle.com, tabba@...gle.com,
        michael.roth@....com, wei.w.wang@...el.com, rppt@...nel.org,
        liam.merwick@...cle.com, isaku.yamahata@...il.com,
        jarkko@...nel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, hughd@...gle.com, brauner@...nel.org
Subject: Re: Rename restrictedmem => guardedmem? (was: Re: [PATCH v10 0/9]
 KVM: mm: fd-based approach for supporting KVM)


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