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Date: Tue, 6 Dec 2022 10:16:03 +0100
From: "Gupta, Pankaj" <pankaj.gupta@....com>
To: Tianyu Lan <ltykernel@...il.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
Hi Tianyu,
Some minor nits below.
> 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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