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Message-ID: <bb66e339-61db-6c0b-4e39-22bfd70073fd@gmail.com>
Date: Thu, 8 Dec 2022 21:04:10 +0800
From: Tianyu Lan <ltykernel@...il.com>
To: "Gupta, Pankaj" <pankaj.gupta@....com>, luto@...nel.org,
tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
seanjc@...gle.com, pbonzini@...hat.com, jgross@...e.com,
tiala@...rosoft.com, kirill@...temov.name,
jiangshan.ljs@...group.com, peterz@...radead.org,
ashish.kalra@....com, srutherford@...gle.com,
akpm@...ux-foundation.org, anshuman.khandual@....com,
pawan.kumar.gupta@...ux.intel.com, adrian.hunter@...el.com,
daniel.sneddon@...ux.intel.com, alexander.shishkin@...ux.intel.com,
sandipan.das@....com, ray.huang@....com, brijesh.singh@....com,
michael.roth@....com, thomas.lendacky@....com,
venu.busireddy@...cle.com, sterritt@...gle.com,
tony.luck@...el.com, samitolvanen@...gle.com, fenghua.yu@...el.com
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
linux-hyperv@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH V2 01/18] x86/sev: Pvalidate memory gab for
decompressing kernel
On 12/6/2022 5:16 PM, Gupta, Pankaj wrote:
> Hi Tianyu,
>
> Some minor nits below.
>
Thanks a lot to review. I will change these in the next version.
>> Pvalidate needed pages for decompressing kernel. The E820_TYPE_RAM
>> entry includes only validated memory. The kernel expects that the
>> RAM entry's addr is fixed while the entry size is to be extended
>> to cover addresses to the start of next entry. This patch increases
>> the RAM entry size to cover all possilble memory addresses until
>
> s/possilble/possible
>
>> init_size.
>>
>> Signed-off-by: Tianyu Lan <tiala@...rosoft.com>
>> ---
>> arch/x86/boot/compressed/head_64.S | 8 +++
>> arch/x86/boot/compressed/sev.c | 84 ++++++++++++++++++++++++++++++
>> 2 files changed, 92 insertions(+)
>>
>> diff --git a/arch/x86/boot/compressed/head_64.S
>> b/arch/x86/boot/compressed/head_64.S
>> index d33f060900d2..818edaf5d0cf 100644
>> --- a/arch/x86/boot/compressed/head_64.S
>> +++ b/arch/x86/boot/compressed/head_64.S
>> @@ -348,6 +348,14 @@ SYM_CODE_START(startup_64)
>> cld
>> cli
>> +#ifdef CONFIG_AMD_MEM_ENCRYPT
>> + /* pvalidate memory on demand if SNP is enabled. */
>> + pushq %rsi
>> + movq %rsi, %rdi
>> + call pvalidate_for_startup_64
>> + popq %rsi
>> +#endif
>> +
>> /* Setup data segments. */
>> xorl %eax, %eax
>> movl %eax, %ds
>> diff --git a/arch/x86/boot/compressed/sev.c
>> b/arch/x86/boot/compressed/sev.c
>> index 960968f8bf75..3a5a1ab16095 100644
>> --- a/arch/x86/boot/compressed/sev.c
>> +++ b/arch/x86/boot/compressed/sev.c
>> @@ -12,8 +12,10 @@
>> */
>> #include "misc.h"
>> +#include <asm/msr-index.h>
>> #include <asm/pgtable_types.h>
>> #include <asm/sev.h>
>> +#include <asm/svm.h>
>> #include <asm/trapnr.h>
>> #include <asm/trap_pf.h>
>> #include <asm/msr-index.h>
>> @@ -21,6 +23,7 @@
>> #include <asm/ptrace.h>
>> #include <asm/svm.h>
>> #include <asm/cpuid.h>
>> +#include <asm/e820/types.h>
>> #include "error.h"
>> #include "../msr.h"
>> @@ -117,6 +120,22 @@ static enum es_result vc_read_mem(struct
>> es_em_ctxt *ctxt,
>> /* Include code for early handlers */
>> #include "../../kernel/sev-shared.c"
>> +/* Check SEV-SNP via MSR */
>> +static bool sev_snp_runtime_check(void)
>> +{
>> + unsigned long low, high;
>> + u64 val;
>> +
>> + asm volatile("rdmsr\n" : "=a" (low), "=d" (high) :
>> + "c" (MSR_AMD64_SEV));
>> +
>> + val = (high << 32) | low;
>> + if (val & MSR_AMD64_SEV_SNP_ENABLED)
>> + return true;
>> +
>> + return false;
>> +}
>> +
>> static inline bool sev_snp_enabled(void)
>> {
>> return sev_status & MSR_AMD64_SEV_SNP_ENABLED;
>> @@ -456,3 +475,68 @@ void sev_prep_identity_maps(unsigned long
>> top_level_pgt)
>> sev_verify_cbit(top_level_pgt);
>> }
>> +
>> +static void extend_e820_on_demand(struct boot_e820_entry *e820_entry,
>> + u64 needed_ram_end)
>> +{
>> + u64 end, paddr;
>> + unsigned long eflags;
>> + int rc;
>> +
>> + if (!e820_entry)
>> + return;
>> +
>> + /* Validated memory must be aligned by PAGE_SIZE. */
>> + end = ALIGN(e820_entry->addr + e820_entry->size, PAGE_SIZE);
>> + if (needed_ram_end > end && e820_entry->type == E820_TYPE_RAM) {
>
> maybe "if check" can be used to return from here, would read code better?
>
>> + for (paddr = end; paddr < needed_ram_end; paddr += PAGE_SIZE)
> Maybe we could reuse 'pvalidate_pages' here?
>
>> + rc = pvalidate(paddr, RMP_PG_SIZE_4K, true);
>> + if (rc) {
>> + error("Failed to validate address.n");
>
> Would it make sense to print the cause of failure here?
>
>> + return;
>> + }
>> + }
>> + e820_entry->size = needed_ram_end - e820_entry->addr;
>> + }
>> +}
>> +
>> +/*
>> + * Explicitly pvalidate needed pages for decompressing the kernel.
>> + * The E820_TYPE_RAM entry includes only validated memory. The kernel
>> + * expects that the RAM entry's addr is fixed while the entry size is
>> to be
>> + * extended to cover addresses to the start of next entry.
>> + * The function increases the RAM entry size to cover all possible
>> memory
>> + * addresses until init_size.
>> + * For example, init_end = 0x4000000,
>> + * [RAM: 0x0 - 0x0], M[RAM: 0x0 - 0xa0000]
>> + * [RSVD: 0xa0000 - 0x10000] [RSVD: 0xa0000 - 0x10000]
>> + * [ACPI: 0x10000 - 0x20000] ==> [ACPI: 0x10000 - 0x20000]
>> + * [RSVD: 0x800000 - 0x900000] [RSVD: 0x800000 - 0x900000]
>> + * [RAM: 0x1000000 - 0x2000000] M[RAM: 0x1000000 - 0x2001000]
>> + * [RAM: 0x2001000 - 0x2007000] M[RAM: 0x2001000 - 0x4000000]
>> + * Other RAM memory after init_end is pvalidated by
>> ms_hyperv_init_platform
>> + */
>> +__visible void pvalidate_for_startup_64(struct boot_params *boot_params)
>> +{
>> + struct boot_e820_entry *e820_entry;
>> + u64 init_end =
>> + boot_params->hdr.pref_address + boot_params->hdr.init_size;
>> + u8 i, nr_entries = boot_params->e820_entries;
>> + u64 needed_end;
>
> Could not very well interpret the name 'needed_end'.
>
>> +
>> + if (!sev_snp_runtime_check())
>> + return;
>> +
>> + for (i = 0; i < nr_entries; ++i) {
>> + /* Pvalidate memory holes in e820 RAM entries. */
>
> Pvalidate and pvalidate names are used interchangeably in comments.
>
>> + e820_entry = &boot_params->e820_table[i];
>> + if (i < nr_entries - 1) {
>> + needed_end = boot_params->e820_table[i + 1].addr;
>> + if (needed_end < e820_entry->addr)
>> + error("e820 table is not sorted.\n");
>> + } else {
>> + needed_end = init_end;
>> + }
>> + extend_e820_on_demand(e820_entry, needed_end);
>> + }
>> +}
>
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