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Shutemov" To: Vlastimil Babka Cc: Michael Roth , Borislav Petkov , Andy Lutomirski , Dave Hansen , Sean Christopherson , Andrew Morton , Joerg Roedel , Ard Biesheuvel , Andi Kleen , Kuppuswamy Sathyanarayanan , David Rientjes , Tom Lendacky , Thomas Gleixner , Peter Zijlstra , Paolo Bonzini , Ingo Molnar , Dario Faggioli , Mike Rapoport , David Hildenbrand , Mel Gorman , marcelo.cerri@canonical.com, tim.gardner@canonical.com, khalid.elmously@canonical.com, philip.cox@canonical.com, aarcange@redhat.com, peterx@redhat.com, x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv14 5/9] efi: Add unaccepted memory support Message-ID: <20231013172728.66pm7os3fp7laxwr@box> References: <20230606142637.5171-1-kirill.shutemov@linux.intel.com> <20230606142637.5171-6-kirill.shutemov@linux.intel.com> <20231010210518.jguawj7bscwgvszv@amd.com> <20231013123358.y4pcdp5fgtt4ax6g@box.shutemov.name> <20231013162210.bqepgz6wnh7uohqq@box> <34d94c58-f5f3-48eb-5833-0ef0c90cf868@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <34d94c58-f5f3-48eb-5833-0ef0c90cf868@suse.cz> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 1851F40026 X-Stat-Signature: 7ahcebtf95o881p4bgd4dsps981j9ieu X-Rspam-User: X-HE-Tag: 1697218061-289481 X-HE-Meta: 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 8+H6ioPc VecLVRo6s7u9xf7wIpQU6GvGMBeuicULNpafb8ktEnw5Hz8cQkIw10cyeBYuSIrjfcdkxYZJnI1Uu7jp1e5RsT4PAHdh07M9aGy/fENoMWnQNhFc8f2vztFFh7/tcFgK3sC2J 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: On Fri, Oct 13, 2023 at 06:44:45PM +0200, Vlastimil Babka wrote: > On 10/13/23 18:22, Kirill A. Shutemov wrote: > > On Fri, Oct 13, 2023 at 03:33:58PM +0300, Kirill A. Shutemov wrote: > >> > While testing SNP guests running today's tip/master (ef19bc9dddc3) I ran > >> > into what seems to be fairly significant lock contention due to the > >> > unaccepted_memory_lock spinlock above, which results in a constant stream > >> > of soft-lockups until the workload gets all its memory accepted/faulted > >> > in if the guest has around 16+ vCPUs. > >> > > >> > I've included the guest dmesg traces I was seeing below. > >> > > >> > In this case I was running a 32 vCPU guest with 200GB of memory running on > >> > a 256 thread EPYC (Milan) system, and can trigger the above situation fairly > >> > reliably by running the following workload in a freshly-booted guests: > >> > > >> > stress --vm 32 --vm-bytes 5G --vm-keep > >> > > >> > Scaling up the number of stress threads and vCPUs should make it easier > >> > to reproduce. > >> > > >> > Other than unresponsiveness/lockup messages until the memory is accepted, > >> > the guest seems to continue running fine, but for large guests where > >> > unaccepted memory is more likely to be useful, it seems like it could be > >> > an issue, especially when consider 100+ vCPU guests. > >> > >> Okay, sorry for delay. It took time to reproduce it with TDX. > >> > >> I will look what can be done. > > > > Could you check if the patch below helps? > > > > diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c > > index 853f7dc3c21d..591da3f368fa 100644 > > --- a/drivers/firmware/efi/unaccepted_memory.c > > +++ b/drivers/firmware/efi/unaccepted_memory.c > > @@ -8,6 +8,14 @@ > > /* Protects unaccepted memory bitmap */ > > static DEFINE_SPINLOCK(unaccepted_memory_lock); > > > > +struct accept_range { > > + struct list_head list; > > + unsigned long start; > > + unsigned long end; > > +}; > > + > > +static LIST_HEAD(accepting_list); > > + > > /* > > * accept_memory() -- Consult bitmap and accept the memory if needed. > > * > > @@ -24,6 +32,7 @@ void accept_memory(phys_addr_t start, phys_addr_t end) > > { > > struct efi_unaccepted_memory *unaccepted; > > unsigned long range_start, range_end; > > + struct accept_range range, *entry; > > unsigned long flags; > > u64 unit_size; > > > > @@ -80,7 +89,25 @@ void accept_memory(phys_addr_t start, phys_addr_t end) > > > > range_start = start / unit_size; > > > > + range.start = start; > > + range.end = end; > > +retry: > > spin_lock_irqsave(&unaccepted_memory_lock, flags); > > + > > + list_for_each_entry(entry, &accepting_list, list) { > > + if (entry->end < start) > > + continue; > > + if (entry->start > end) > > + continue; > > + spin_unlock_irqrestore(&unaccepted_memory_lock, flags); > > + > > + /* Somebody else accepting the range */ > > + cpu_relax(); > > Should this be rather cond_resched()? I think cpu_relax() isn't enough to > prevent soft lockups. Right. For some reason, I thought we cannot call cond_resched() from atomic context (we sometimes get there from atomic context), but we can. > Although IIUC hitting this should be rare, as the contending tasks will pick > different ranges via try_to_accept_memory_one(), right? Yes, it should be rare. Generally, with exception of memblock, we accept all memory with MAX_ORDER chunks. As long as unit_size <= MAX_ORDER page allocator should never trigger the conflict as the caller owns full range to accept. I will test the idea with larger unit_size to see how it behaves. -- Kiryl Shutsemau / Kirill A. Shutemov