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[2003:cb:c718:100:347d:db94:161d:398f]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4396180f199sm26455445e9.15.2025.02.13.12.33.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Feb 2025 12:34:00 -0800 (PST) Message-ID: <570b2f04-0c46-4a40-9b59-b9db1b5b6185@redhat.com> Date: Thu, 13 Feb 2025 21:33:58 +0100 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/2] KVM: s390: pv: fix race when making a page secure From: David Hildenbrand To: Claudio Imbrenda , kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, frankja@linux.ibm.com, borntraeger@de.ibm.com, nrb@linux.ibm.com, seiden@linux.ibm.com, nsg@linux.ibm.com, schlameuss@linux.ibm.com, hca@linux.ibm.com References: <20250213200755.196832-1-imbrenda@linux.ibm.com> <20250213200755.196832-3-imbrenda@linux.ibm.com> <6c741da9-a793-4a59-920f-8df77807bc4d@redhat.com> Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <6c741da9-a793-4a59-920f-8df77807bc4d@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 13.02.25 21:16, David Hildenbrand wrote: > On 13.02.25 21:07, Claudio Imbrenda wrote: >> Holding the pte lock for the page that is being converted to secure is >> needed to avoid races. A previous commit removed the locking, which >> caused issues. Fix by locking the pte again. >> >> Fixes: 5cbe24350b7d ("KVM: s390: move pv gmap functions into kvm") > > If you found this because of my report about the changed locking, > consider adding a Suggested-by / Reported-y. > >> Signed-off-by: Claudio Imbrenda >> --- >> arch/s390/include/asm/uv.h | 2 +- >> arch/s390/kernel/uv.c | 19 +++++++++++++++++-- >> arch/s390/kvm/gmap.c | 12 ++++++++---- >> 3 files changed, 26 insertions(+), 7 deletions(-) >> >> diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h >> index b11f5b6d0bd1..46fb0ef6f984 100644 >> --- a/arch/s390/include/asm/uv.h >> +++ b/arch/s390/include/asm/uv.h >> @@ -631,7 +631,7 @@ int uv_pin_shared(unsigned long paddr); >> int uv_destroy_folio(struct folio *folio); >> int uv_destroy_pte(pte_t pte); >> int uv_convert_from_secure_pte(pte_t pte); >> -int make_folio_secure(struct folio *folio, struct uv_cb_header *uvcb); >> +int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header *uvcb); >> int uv_convert_from_secure(unsigned long paddr); >> int uv_convert_from_secure_folio(struct folio *folio); >> >> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c >> index 9f05df2da2f7..de3c092da7b9 100644 >> --- a/arch/s390/kernel/uv.c >> +++ b/arch/s390/kernel/uv.c >> @@ -245,7 +245,7 @@ static int expected_folio_refs(struct folio *folio) >> * Context: The caller must hold exactly one extra reference on the folio >> * (it's the same logic as split_folio()) >> */ >> -int make_folio_secure(struct folio *folio, struct uv_cb_header *uvcb) >> +static int __make_folio_secure(struct folio *folio, unsigned long hva, struct uv_cb_header *uvcb) >> { >> int expected, cc = 0; >> >> @@ -277,7 +277,22 @@ int make_folio_secure(struct folio *folio, struct uv_cb_header *uvcb) >> return -EAGAIN; >> return uvcb->rc == 0x10a ? -ENXIO : -EINVAL; >> } >> -EXPORT_SYMBOL_GPL(make_folio_secure); >> + >> +int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header *uvcb) >> +{ >> + spinlock_t *ptelock; >> + pte_t *ptep; >> + int rc; >> + >> + ptep = get_locked_pte(mm, hva, &ptelock); >> + if (!ptep) >> + return -ENXIO; >> + rc = __make_folio_secure(page_folio(pte_page(*ptep)), hva, uvcb); >> + pte_unmap_unlock(ptep, ptelock); >> + >> + return rc; >> +} >> +EXPORT_SYMBOL_GPL(make_hva_secure); >> >> /* >> * To be called with the folio locked or with an extra reference! This will >> diff --git a/arch/s390/kvm/gmap.c b/arch/s390/kvm/gmap.c >> index fc4d490d25a2..e56c0ab5fec7 100644 >> --- a/arch/s390/kvm/gmap.c >> +++ b/arch/s390/kvm/gmap.c >> @@ -55,7 +55,7 @@ static bool should_export_before_import(struct uv_cb_header *uvcb, struct mm_str >> return atomic_read(&mm->context.protected_count) > 1; >> } >> >> -static int __gmap_make_secure(struct gmap *gmap, struct page *page, void *uvcb) >> +static int __gmap_make_secure(struct gmap *gmap, struct page *page, unsigned long hva, void *uvcb) >> { >> struct folio *folio = page_folio(page); >> int rc; >> @@ -83,7 +83,7 @@ static int __gmap_make_secure(struct gmap *gmap, struct page *page, void *uvcb) >> return -EAGAIN; >> if (should_export_before_import(uvcb, gmap->mm)) >> uv_convert_from_secure(folio_to_phys(folio)); >> - rc = make_folio_secure(folio, uvcb); >> + rc = make_hva_secure(gmap->mm, hva, uvcb); >> folio_unlock(folio); >> >> /* >> @@ -120,6 +120,7 @@ static int __gmap_make_secure(struct gmap *gmap, struct page *page, void *uvcb) >> int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb) >> { >> struct kvm *kvm = gmap->private; >> + unsigned long vmaddr; >> struct page *page; >> int rc = 0; >> >> @@ -127,8 +128,11 @@ int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb) >> >> page = gfn_to_page(kvm, gpa_to_gfn(gaddr)); >> mmap_read_lock(gmap->mm); >> - if (page) >> - rc = __gmap_make_secure(gmap, page, uvcb); >> + vmaddr = gfn_to_hva(gmap->private, gpa_to_gfn(gaddr)); >> + if (kvm_is_error_hva(vmaddr)) >> + rc = -ENXIO; >> + if (!rc && page) >> + rc = __gmap_make_secure(gmap, page, vmaddr, uvcb); >> kvm_release_page_clean(page); >> mmap_read_unlock(gmap->mm); >> > > You effectively make the code more complicated and inefficient than > before. Now you effectively walk the page table twice in the common > small-folio case ... > > Can we just go back to the old handling that we had before here? I'll note that there is still the possibility for a different race: nothing guarantees that the page you looked up using gfn_to_hva() will still be mapped when you perform the get_locked_pte(). Not sure what would happen if we would have a different page mapped. You could re-verify it is still there, but then, doing two page table walks is still more than required in the common case where we can just perform the conversion. -- Cheers, David / dhildenb