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Date: Thu, 6 Sep 2018 13:50:21 -0500 From: Brijesh Singh <brijesh.singh@....com> To: Sean Christopherson <sean.j.christopherson@...el.com> Cc: brijesh.singh@....com, x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org, Tom Lendacky <thomas.lendacky@....com>, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...e.de>, "H. Peter Anvin" <hpa@...or.com>, Paolo Bonzini <pbonzini@...hat.com>, Radim Krčmář <rkrcmar@...hat.com> Subject: Re: [PATCH v5 5/5] x86/kvm: Avoid dynamic allocation of pvclock data when SEV is active On 09/06/2018 09:07 AM, Sean Christopherson wrote: ... >> + >> +/* This should cover upto 512 VCPUS (first 64 are covered by hv_clock_boot[]). */ >> +#define HVC_DECRYPTED_ARRAY_SIZE \ >> + ((PAGE_SIZE * 7) / sizeof(struct pvclock_vsyscall_time_info)) > > I think we can define the size relative to NR_CPUS rather than picking > an arbitrary number of pages, maybe with a BUILD_BUG_ON to make sure > the total size won't require a second 2mb page for __decrpyted. > > #define HVC_DECRYPTED_ARRAY_SIZE \ > PAGE_ALIGN((NR_CPUS - HVC_BOOT_ARRAY_SIZE) * \ > sizeof(struct pvclock_vsyscall_time_info)) > Sure works for me. >> +static struct pvclock_vsyscall_time_info >> + hv_clock_dec[HVC_DECRYPTED_ARRAY_SIZE] __decrypted_hvclock; >> + >> static inline struct pvclock_vcpu_time_info *this_cpu_pvti(void) >> { >> return &this_cpu_read(hv_clock_per_cpu)->pvti; >> @@ -267,10 +274,19 @@ static int kvmclock_setup_percpu(unsigned int cpu) >> return 0; >> >> /* Use the static page for the first CPUs, allocate otherwise */ >> - if (cpu < HVC_BOOT_ARRAY_SIZE) >> + if (cpu < HVC_BOOT_ARRAY_SIZE) { >> p = &hv_clock_boot[cpu]; >> - else >> - p = kzalloc(sizeof(*p), GFP_KERNEL); >> + } else { >> + /* >> + * When SEV is active, use the static pages from >> + * .data..decrypted_hvclock section. The pages are already >> + * mapped with C=0. >> + */ >> + if (sev_active()) >> + p = &hv_clock_dec[cpu - HVC_BOOT_ARRAY_SIZE]; >> + else >> + p = kzalloc(sizeof(*p), GFP_KERNEL); >> + } > > Personal preference, but I think an if-elif-else with a single block > comment would be easier to read. I can do with that. thanks for your feedback. > > /* > * Blah blah blah > */ > if (cpu < HVC_BOOT_ARRAY_SIZE) > p = &hv_clock_boot[cpu]; > else if (sev_active()) > p = &hv_clock_dec[cpu - HVC_BOOT_ARRAY_SIZE]; > else > p = kzalloc(sizeof(*p), GFP_KERNEL); >
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