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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240731_031124_026944_CD0B8DBC X-CRM114-Status: GOOD ( 21.52 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 7/30/24 22:15, Sean Christopherson wrote: > On Tue, Jul 30, 2024, Paolo Bonzini wrote: >> On 7/27/24 01:51, Sean Christopherson wrote: >>> Add a kvm_follow_pfn() wrapper, kvm_lookup_pfn(), to allow looking up a >>> gfn=>pfn mapping without the caller getting a reference to any underlying >>> page. The API will be used in flows that want to know if a gfn points at >>> a valid pfn, but don't actually need to do anything with the pfn. >> >> Can you rename the function kvm_gfn_has_pfn(), or kvm_gfn_can_be_mapped(), >> and make it return a bool? > > Heh, sure. I initially planned on having it return a bool, but I couldn't figure > out a name, mainly because the kernel's pfn_valid() makes things like > kvm_gfn_has_valid_pfn() confusing/misleading :-( > >> (As an aside, I wonder if reexecute_instruction() could just use >> kvm_is_error_hva(kvm_vcpu_gfn_to_hva(vcpu, gpa_to_gfn(gpa)) instead of going >> all the way to a pfn. But it's ok to be more restrictive). > > Heh #2, I wondered the same thing. I think it would work? Verifying that there's > a usable pfn also protects against retrying an access that hit -EHWPOISON, but I'm > prety sure that would require a rare race, and I don't think it could result in > the guest being put into an infinite loop. Indeed, and even the check in kvm_alloc_apic_access_page() is totally useless. The page can go away at any time between the call and vmx_set_apic_access_page_addr() or, for AMD, the #NPF on APIC_DEFAULT_PHYS_BASE. Yes, it's verifying that the system isn't under extreme memory pressure, but in practice a 4K get_user_pages is never going to fail, it's just going to cause something else to be swapped. I'd just get rid of both of them, so there's no need for kvm_lookup_pfn(). Paolo