Re: [PATCH v3] x86/sev: Make enc_dec_hypercall() accept a size instead of npages

On Thu, Aug 24, 2023 at 3:37 PM Steve Rutherford srutherford@google.com wrote:

enc_dec_hypercall() accepted a page count instead of a size, which forced its callers to round up. As a result, non-page aligned vaddrs caused pages to be spuriously marked as decrypted via the encryption status hypercall, which in turn caused consistent corruption of pages during live migration. Live migration requires accurate encryption status information to avoid migrating pages from the wrong perspective.

Cc: stable@vger.kernel.org Fixes: 064ce6c550a0 ("mm: x86: Invoke hypercall when page encryption status is changed") Signed-off-by: Steve Rutherford srutherford@google.com Reviewed-by: Tom Lendacky thomas.lendacky@amd.com Reviewed-by: Pankaj Gupta pankaj.gupta@amd.com

Ran test comparing the c-bit status in the guest page tables to the host perspective. Before the patch, there was a c-bit status mismatch. Adding the patch fixed these mismatched c-bits. Tested-by: Ben Hillier bhillier@google.com

---

arch/x86/include/asm/mem_encrypt.h | 6 +++--- arch/x86/kernel/kvm.c | 4 +--- arch/x86/mm/mem_encrypt_amd.c | 13 ++++++------- 3 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h index 7f97a8a97e24..473b16d73b47 100644 --- a/arch/x86/include/asm/mem_encrypt.h +++ b/arch/x86/include/asm/mem_encrypt.h @@ -50,8 +50,8 @@ void __init sme_enable(struct boot_params *bp);

int __init early_set_memory_decrypted(unsigned long vaddr, unsigned long size); int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size); -void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages,

•                                       bool enc);
  

+void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr,

•                                       unsigned long size, bool enc);
  
  

void __init mem_encrypt_free_decrypted_mem(void);

@@ -85,7 +85,7 @@ early_set_memory_decrypted(unsigned long vaddr, unsigned long size) { return 0; static inline int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size) { return 0; } static inline void __init -early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages, bool enc) {} +early_set_mem_enc_dec_hypercall(unsigned long vaddr, unsigned long size, bool enc) {}

static inline void mem_encrypt_free_decrypted_mem(void) { }

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 6a36db4f79fd..b8ab9ee5896c 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -966,10 +966,8 @@ static void __init kvm_init_platform(void) * Ensure that _bss_decrypted section is marked as decrypted in the * shared pages list. */

•           nr_pages = DIV_ROUND_UP(__end_bss_decrypted - __start_bss_decrypted,
  

•                                   PAGE_SIZE);
            early_set_mem_enc_dec_hypercall((unsigned long)__start_bss_decrypted,
  

•                                           nr_pages, 0);
  

•                                           __end_bss_decrypted - __start_bss_decrypted, 0);
  
            /*
             * If not booted using EFI, enable Live migration support.
  

diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c index 54bbd5163e8d..6faea41e99b6 100644 --- a/arch/x86/mm/mem_encrypt_amd.c +++ b/arch/x86/mm/mem_encrypt_amd.c @@ -288,11 +288,10 @@ static bool amd_enc_cache_flush_required(void) return !cpu_feature_enabled(X86_FEATURE_SME_COHERENT); }

-static void enc_dec_hypercall(unsigned long vaddr, int npages, bool enc) +static void enc_dec_hypercall(unsigned long vaddr, unsigned long size, bool enc) { #ifdef CONFIG_PARAVIRT

•   unsigned long sz = npages << PAGE_SHIFT;
  

•   unsigned long vaddr_end = vaddr + sz;
  

•   unsigned long vaddr_end = vaddr + size;
  
    while (vaddr < vaddr_end) {
            int psize, pmask, level;
  

@@ -342,7 +341,7 @@ static bool amd_enc_status_change_finish(unsigned long vaddr, int npages, bool e snp_set_memory_private(vaddr, npages);

    if (!cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))

•           enc_dec_hypercall(vaddr, npages, enc);
  

•           enc_dec_hypercall(vaddr, npages << PAGE_SHIFT, enc);
  
    return true;
  

} @@ -466,7 +465,7 @@ static int __init early_set_memory_enc_dec(unsigned long vaddr,

    ret = 0;

•   early_set_mem_enc_dec_hypercall(start, PAGE_ALIGN(size) >> PAGE_SHIFT, enc);
  

•   early_set_mem_enc_dec_hypercall(start, size, enc);
  

out: __flush_tlb_all(); return ret; @@ -482,9 +481,9 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size) return early_set_memory_enc_dec(vaddr, size, true); }

-void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr, int npages, bool enc) +void __init early_set_mem_enc_dec_hypercall(unsigned long vaddr, unsigned long size, bool enc) {

•   enc_dec_hypercall(vaddr, npages, enc);
  

•   enc_dec_hypercall(vaddr, size, enc);
  

}

void __init sme_early_init(void)

2.42.0.rc1.204.g551eb34607-goog