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From: Roman Gushchin To: Matthew Wilcox Cc: Andrew Morton , linux-mm@kvack.org, Vlastimil Babka , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Hugh Dickins Subject: Re: [PATCH v2] mm: page_alloc: move mlocked flag clearance into free_pages_prepare() Message-ID: References: <20241021173455.2691973-1-roman.gushchin@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Stat-Signature: z5p5g85no35q4fbdzodnjpmm7wghnerz X-Rspamd-Queue-Id: 201CA100015 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1729571609-238959 X-HE-Meta: U2FsdGVkX1/QM1PC7zwYx0/0bM3WyQltgz/gusHsIg6GrPT8HSUKZVbhH57QDRW2NWJjrmkRicynds5V0hFW1j+0NmcHWiLjwn7iO6O/BwWu0urTf9PxImF0hxtdxJ9tikSI9/X7gipW8v1yhisvc54KwHqgmcMlbKaqu9SkaPvWNY40bRMHoIKTJJMB4gWdhUeGkfWp1AzN2fJK6RcEWNDyLh7SFtmcs4S+wUxoaoU+bw3zNICa1/ZjD9beoA5btJz6A9iP3RFCwnVdH/3uBDUPUdEriik29qxDHrJ+EcLcv5whNs55/e5rFAW+fvWfm0iYFOlCDsMqPlVd5D4MV6mb6wr7nWsLL80mTBOdH+4RU+v3rX+eck8NvCzA1lYfny9hXqLUR7QuLEnWtkF9XF7Ojs6murLUTdkvXOumJOIxffKkqYkMbxudcJQePC7ng8LZklqQEhyeg4g6DYysvrcrX2ph3ob3F09NAE+WCwRBhgFZ1gba/z9GDQM21+HH1+m58KtPb80/Vdn0puGPzcop83jF3LXSrz17qOA/cbz+KDmblf886GM4xt3qQKSQ1Sc2AH9lyOmvxyZSyKpenKd+ePrFCoHlMM+3l8vtYibVN/LJgi+jP36g7WVwgBHmSn3xMptl4uEEGncVykSCtRupkBo5Evm/1SZJ0h/RvkMRVU9m00yl4kLnjDAHbwmymMEFpC1j+5959pTIcHO4A2RtFDEpP+666zHtoa1z2gVhReNy94Spk8Y9aPNNCixadqPX+boY7zZcW02edUKmISUyFCoMblS9pY8A+C3FYKvIHqisKs/T4eHP5eC9YuHo03Or63hPAm3zAcmTJL3tDItrof9PTENpMvixaDJD7GZ3oiv02awsnHiTjW5NutIxkZIC4EtGOej4omJ+VMpRDyiGSJGxi5kgsyDUsMJsAs0+WCAvzZES0qdFEpS28LtMu3ixQyniCebC/zYwPJ3 crXLf17X fTVjNzW3J0Ya6XZe+U72Gz9jOM+2WqVY6iWcElFDkpBXc7B99/+cyBS8v2GgwRxXg98OLPB0dbEGu0weMCjpfheI1KWr8RX9usaSuYBKtbkY+ZLHgs0edUH6l3ECPWZrIf7d6PQXMwjPKU5sCeCmUsUo4KgbfiRo+Mopd8AbC1cul1Olu1GYgo0cB8FVka39z96MTzDcIccudNE1yw8vSKdZxjQHF57yED6k7 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Oct 22, 2024 at 04:47:19AM +0100, Matthew Wilcox wrote: > On Tue, Oct 22, 2024 at 02:14:39AM +0000, Roman Gushchin wrote: > > On Mon, Oct 21, 2024 at 09:34:24PM +0100, Matthew Wilcox wrote: > > > On Mon, Oct 21, 2024 at 05:34:55PM +0000, Roman Gushchin wrote: > > > > Fix it by moving the mlocked flag clearance down to > > > > free_page_prepare(). > > > > > > Urgh, I don't like this new reference to folio in free_pages_prepare(). > > > It feels like a layering violation. I'll think about where else we > > > could put this. > > > > I agree, but it feels like it needs quite some work to do it in a nicer way, > > no way it can be backported to older kernels. As for this fix, I don't > > have better ideas... > > Well, what is KVM doing that causes this page to get mapped to userspace? > Don't tell me to look at the reproducer as it is 403 Forbidden. All I > can tell is that it's freed with vfree(). > > Is it from kvm_dirty_ring_get_page()? That looks like the obvious thing, > but I'd hate to spend a lot of time on it and then discover I was looking > at the wrong thing. One of the pages is vcpu->run, others belong to kvm->coalesced_mmio_ring. Here is the reproducer: #define _GNU_SOURCE #include #include #include #include #include #include #include #include #include #include #include #ifndef __NR_mlock2 #define __NR_mlock2 325 #endif uint64_t r[3] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff}; #ifndef KVM_CREATE_VM #define KVM_CREATE_VM 0xae01 #endif #ifndef KVM_CREATE_VCPU #define KVM_CREATE_VCPU 0xae41 #endif int main(void) { syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1, /*offset=*/0ul); syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/ 7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1, /*offset=*/0ul); syscall(__NR_mmap, /*addr=*/0x21000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/ 0x32ul, /*fd=*/-1, /*offset=*/0ul); intptr_t res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/"/dev/kvm", /*flags=*/0, /*mode=*/0); if (res != -1) r[0] = res; res = syscall(__NR_ioctl, /*fd=*/r[0], /*cmd=*/KVM_CREATE_VM, /*type=*/0ul); if (res != -1) r[1] = res; res = syscall(__NR_ioctl, /*fd=*/r[1], /*cmd=*/KVM_CREATE_VCPU, /*id=*/0ul); if (res != -1) r[2] = res; syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0xb36000ul, /*prot=PROT_SEM|PROT_WRITE|PROT_READ|PROT_EXEC*/ 0xful, /*flags=MAP_FIXED|MAP_SHARED*/ 0x11ul, /*fd=*/r[2], /*offset=*/0ul); syscall(__NR_mlock2, /*addr=*/0x20000000ul, /*size=*/0x400000ul, /*flags=*/0ul); syscall(__NR_mremap, /*addr=*/0x200ab000ul, /*len=*/0x1000ul, /*newlen=*/0x1000ul, /*flags=MREMAP_DONTUNMAP|MREMAP_FIXED|MREMAP_MAYMOVE*/ 7ul, /*newaddr=*/0x20ffc000ul); return 0; }