linux-kernel - Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM

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Message-ID: <20230128140030.GB700688@chaop.bj.intel.com>
Date:   Sat, 28 Jan 2023 22:00:30 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Arnd Bergmann <arnd@...db.de>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Miaohe Lin <linmiaohe@...wei.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Steven Price <steven.price@....com>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
        ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
        ddutile@...hat.com, dhildenb@...hat.com,
        Quentin Perret <qperret@...gle.com>, tabba@...gle.com,
        Michael Roth <michael.roth@....com>, mhocko@...e.com,
        wei.w.wang@...el.com
Subject: Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE

On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote:
> On Fri, Dec 02, 2022, Chao Peng wrote:
... 
> Strongly prefer to use similar logic to existing code that detects wraps:
> 
> 		mem->restricted_offset + mem->memory_size < mem->restricted_offset
> 
> This is also where I'd like to add the "gfn is aligned to offset" check, though
> my brain is too fried to figure that out right now.

Used count_trailing_zeros() for this TODO, unsure we have other better
approach.

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index afc8c26fa652..fd34c5f7cd2f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -56,6 +56,7 @@
 #include <asm/processor.h>
 #include <asm/ioctl.h>
 #include <linux/uaccess.h>
+#include <linux/count_zeros.h>
 
 #include "coalesced_mmio.h"
 #include "async_pf.h"
@@ -2087,6 +2088,19 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
 	return false;
 }
 
+/*
+ * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa).
+ */
+static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa)
+{
+	if (!offset)
+		return true;
+	if (!gpa)
+		return false;
+
+	return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa));
+}
+
 /*
  * Allocate some memory and give it an address in the guest physical address
  * space.
@@ -2128,7 +2142,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	if (mem->flags & KVM_MEM_PRIVATE &&
 	    (mem->restrictedmem_offset & (PAGE_SIZE - 1) ||
 	     mem->restrictedmem_offset + mem->memory_size < mem->restrictedmem_offset ||
-	     0 /* TODO: require gfn be aligned with restricted offset */))
+	     !kvm_check_rmem_offset_alignment(mem->restrictedmem_offset,
+					      mem->guest_phys_addr)))
 		return -EINVAL;
 	if (as_id >= kvm_arch_nr_memslot_as_ids(kvm) || id >= KVM_MEM_SLOTS_NUM)
 		return -EINVAL;