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Thu, 19 Jun 2025 02:26:11 -0700 (PDT) Message-ID: <9376b309-8561-4fcc-9e71-3bd03fd8f9d0@suse.com> Date: Thu, 19 Jun 2025 12:26:07 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 02/21] x86/virt/tdx: Enhance tdh_mem_page_aug() to support huge pages To: Yan Zhao , "Edgecombe, Rick P" Cc: "pbonzini@redhat.com" , "seanjc@google.com" , "Shutemov, Kirill" , "quic_eberman@quicinc.com" , "Li, Xiaoyao" , "kvm@vger.kernel.org" , "Hansen, Dave" , "david@redhat.com" , "thomas.lendacky@amd.com" , "tabba@google.com" , "Li, Zhiquan1" , "Du, Fan" , "linux-kernel@vger.kernel.org" , "michael.roth@amd.com" , "Weiny, Ira" , "vbabka@suse.cz" , "binbin.wu@linux.intel.com" , "ackerleytng@google.com" , "Yamahata, Isaku" , "Peng, Chao P" , "Annapurve, Vishal" , "jroedel@suse.de" , "Miao, Jun" , "pgonda@google.com" , "x86@kernel.org" References: <20250424030033.32635-1-yan.y.zhao@intel.com> <20250424030428.32687-1-yan.y.zhao@intel.com> From: Nikolay Borisov Content-Language: en-US Autocrypt: addr=nik.borisov@suse.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 5/16/25 12:05, Yan Zhao wrote: > On Wed, May 14, 2025 at 02:52:49AM +0800, Edgecombe, Rick P wrote: >> On Thu, 2025-04-24 at 11:04 +0800, Yan Zhao wrote: >>> Enhance the SEAMCALL wrapper tdh_mem_page_aug() to support huge pages. >>> >>> Verify the validity of the level and ensure that the mapping range is fully >>> contained within the page folio. >>> >>> As a conservative solution, perform CLFLUSH on all pages to be mapped into >>> the TD before invoking the SEAMCALL TDH_MEM_PAGE_AUG. This ensures that any >>> dirty cache lines do not write back later and clobber TD memory. >> >> This should have a brief background on why it doesn't use the arg - what is >> deficient today. Also, an explanation of how it will be used (i.e. what types of >> pages will be passed) > Will do. > >>> >>> Signed-off-by: Xiaoyao Li >>> Signed-off-by: Isaku Yamahata >>> Signed-off-by: Yan Zhao >>> --- >>>  arch/x86/virt/vmx/tdx/tdx.c | 11 ++++++++++- >>>  1 file changed, 10 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c >>> index f5e2a937c1e7..a66d501b5677 100644 >>> --- a/arch/x86/virt/vmx/tdx/tdx.c >>> +++ b/arch/x86/virt/vmx/tdx/tdx.c >>> @@ -1595,9 +1595,18 @@ u64 tdh_mem_page_aug(struct tdx_td *td, u64 gpa, int level, struct page *page, u >>>   .rdx = tdx_tdr_pa(td), >>>   .r8 = page_to_phys(page), >>>   }; >>> + unsigned long nr_pages = 1 << (level * 9); >>> + struct folio *folio = page_folio(page); >>> + unsigned long idx = 0; >>>   u64 ret; >>> >>> - tdx_clflush_page(page); >>> + if (!(level >= TDX_PS_4K && level < TDX_PS_NR) || >>> +     (folio_page_idx(folio, page) + nr_pages > folio_nr_pages(folio))) >>> + return -EINVAL; >> >> Shouldn't KVM not try to map a huge page in this situation? Doesn't seem like a >> job for the SEAMCALL wrapper. > Ok. If the decision is to trust KVM and all potential callers, it's reasonable > to drop those checks. > >>> + >>> + while (nr_pages--) >>> + tdx_clflush_page(nth_page(page, idx++)); >> >> clflush_cache_range() is: >> static void tdx_clflush_page(struct page *page) >> { >> clflush_cache_range(page_to_virt(page), PAGE_SIZE); >> } >> >> So we have loops within loops... Better to add an arg to tdx_clflush_page() or >> add a variant that takes one. > Ok. > > One thing to note is that even with an extra arg, tdx_clflush_page() has to call > clflush_cache_range() page by page because with > "#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)", > page virtual addresses are not necessarily contiguous. > > What about Binbin's proposal [1]? i.e., > > while (nr_pages) > tdx_clflush_page(nth_page(page, --nr_pages)); What's the problem with using: + for (int i = 0; nr_pages; nr_pages--) + tdx_clflush_page(nth_page(page, i++)) The kernel now allows C99-style definition of variables inside a loop + it's clear how many times the loop has to be executed. > > [1] https://lore.kernel.org/all/a7d0988d-037c-454f-bc6b-57e71b357488@linux.intel.com/ > >>> + >>>   ret = seamcall_ret(TDH_MEM_PAGE_AUG, &args); >>> >>>   *ext_err1 = args.rcx; >> >