Date:   Fri, 24 Feb 2023 06:48:53 +0100
From:   Juergen Gross <jgross@...e.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3 10/12] x86/mtrr: use new cache_map in
 mtrr_type_lookup()

On 23.02.23 20:24, Michael Kelley (LINUX) wrote:
> From: Juergen Gross <jgross@...e.com> Sent: Thursday, February 23, 2023 1:33 AM
>>
>> Instead of crawling through the MTRR register state, use the new
>> cache_map for looking up the cache type(s) of a memory region.
>>
>> This allows now to set the uniform parameter according to the
>> uniformity of the cache mode of the region, instead of setting it
>> only if the complete region is mapped by a single MTRR. This now
>> includes even the region covered by the fixed MTRR registers.
>>
>> Make sure uniform is always set.
>>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>> V3:
>> - new patch
>> ---
>>   arch/x86/kernel/cpu/mtrr/generic.c | 223 ++++-------------------------
>>   1 file changed, 28 insertions(+), 195 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c
>> index ca9b8cec81a0..9c9cbf6b56bc 100644
>> --- a/arch/x86/kernel/cpu/mtrr/generic.c
>> +++ b/arch/x86/kernel/cpu/mtrr/generic.c
>> @@ -138,154 +138,6 @@ static u8 get_effective_type(u8 type1, u8 type2)
>>   	return type1;
>>   }
>>
>> -/*
>> - * Check and return the effective type for MTRR-MTRR type overlap.
>> - * Returns true if the effective type is UNCACHEABLE, else returns false
>> - */
>> -static bool check_type_overlap(u8 *prev, u8 *curr)
>> -{
>> -	*prev = *curr = get_effective_type(*curr, *prev);
>> -
>> -	return *prev == MTRR_TYPE_UNCACHABLE;
>> -}
>> -
>> -/**
>> - * mtrr_type_lookup_fixed - look up memory type in MTRR fixed entries
>> - *
>> - * Return the MTRR fixed memory type of 'start'.
>> - *
>> - * MTRR fixed entries are divided into the following ways:
>> - *  0x00000 - 0x7FFFF : This range is divided into eight 64KB sub-ranges
>> - *  0x80000 - 0xBFFFF : This range is divided into sixteen 16KB sub-ranges
>> - *  0xC0000 - 0xFFFFF : This range is divided into sixty-four 4KB sub-ranges
>> - *
>> - * Return Values:
>> - * MTRR_TYPE_(type)  - Matched memory type
>> - * MTRR_TYPE_INVALID - Unmatched
>> - */
>> -static u8 mtrr_type_lookup_fixed(u64 start, u64 end)
>> -{
>> -	int idx;
>> -
>> -	if (start >= 0x100000)
>> -		return MTRR_TYPE_INVALID;
>> -
>> -	/* 0x0 - 0x7FFFF */
>> -	if (start < 0x80000) {
>> -		idx = 0;
>> -		idx += (start >> 16);
>> -		return mtrr_state.fixed_ranges[idx];
>> -	/* 0x80000 - 0xBFFFF */
>> -	} else if (start < 0xC0000) {
>> -		idx = 1 * 8;
>> -		idx += ((start - 0x80000) >> 14);
>> -		return mtrr_state.fixed_ranges[idx];
>> -	}
>> -
>> -	/* 0xC0000 - 0xFFFFF */
>> -	idx = 3 * 8;
>> -	idx += ((start - 0xC0000) >> 12);
>> -	return mtrr_state.fixed_ranges[idx];
>> -}
>> -
>> -/**
>> - * mtrr_type_lookup_variable - look up memory type in MTRR variable entries
>> - *
>> - * Return Value:
>> - * MTRR_TYPE_(type) - Matched memory type or default memory type (unmatched)
>> - *
>> - * Output Arguments:
>> - * repeat - Set to 1 when [start:end] spanned across MTRR range and type
>> - *	    returned corresponds only to [start:*partial_end].  Caller has
>> - *	    to lookup again for [*partial_end:end].
>> - *
>> - * uniform - Set to 1 when an MTRR covers the region uniformly, i.e. the
>> - *	     region is fully covered by a single MTRR entry or the default
>> - *	     type.
>> - */
>> -static u8 mtrr_type_lookup_variable(u64 start, u64 end, u64 *partial_end,
>> -				    int *repeat, u8 *uniform)
>> -{
>> -	int i;
>> -	u64 base, mask;
>> -	u8 prev_match, curr_match;
>> -
>> -	*repeat = 0;
>> -	*uniform = 1;
>> -
>> -	prev_match = MTRR_TYPE_INVALID;
>> -	for (i = 0; i < num_var_ranges; ++i) {
>> -		unsigned short start_state, end_state, inclusive;
>> -
>> -		if (!(mtrr_state.var_ranges[i].mask_lo & (1 << 11)))
>> -			continue;
>> -
>> -		base = (((u64)mtrr_state.var_ranges[i].base_hi) << 32) +
>> -		       (mtrr_state.var_ranges[i].base_lo & PAGE_MASK);
>> -		mask = (((u64)mtrr_state.var_ranges[i].mask_hi) << 32) +
>> -		       (mtrr_state.var_ranges[i].mask_lo & PAGE_MASK);
>> -
>> -		start_state = ((start & mask) == (base & mask));
>> -		end_state = ((end & mask) == (base & mask));
>> -		inclusive = ((start < base) && (end > base));
>> -
>> -		if ((start_state != end_state) || inclusive) {
>> -			/*
>> -			 * We have start:end spanning across an MTRR.
>> -			 * We split the region into either
>> -			 *
>> -			 * - start_state:1
>> -			 * (start:mtrr_end)(mtrr_end:end)
>> -			 * - end_state:1
>> -			 * (start:mtrr_start)(mtrr_start:end)
>> -			 * - inclusive:1
>> -			 * (start:mtrr_start)(mtrr_start:mtrr_end)(mtrr_end:end)
>> -			 *
>> -			 * depending on kind of overlap.
>> -			 *
>> -			 * Return the type of the first region and a pointer
>> -			 * to the start of next region so that caller will be
>> -			 * advised to lookup again after having adjusted start
>> -			 * and end.
>> -			 *
>> -			 * Note: This way we handle overlaps with multiple
>> -			 * entries and the default type properly.
>> -			 */
>> -			if (start_state)
>> -				*partial_end = base + get_mtrr_size(mask);
>> -			else
>> -				*partial_end = base;
>> -
>> -			if (unlikely(*partial_end <= start)) {
>> -				WARN_ON(1);
>> -				*partial_end = start + PAGE_SIZE;
>> -			}
>> -
>> -			end = *partial_end - 1; /* end is inclusive */
>> -			*repeat = 1;
>> -			*uniform = 0;
>> -		}
>> -
>> -		if ((start & mask) != (base & mask))
>> -			continue;
>> -
>> -		curr_match = mtrr_state.var_ranges[i].base_lo & 0xff;
>> -		if (prev_match == MTRR_TYPE_INVALID) {
>> -			prev_match = curr_match;
>> -			continue;
>> -		}
>> -
>> -		*uniform = 0;
>> -		if (check_type_overlap(&prev_match, &curr_match))
>> -			return curr_match;
>> -	}
>> -
>> -	if (prev_match != MTRR_TYPE_INVALID)
>> -		return prev_match;
>> -
>> -	return mtrr_state.def_type;
>> -}
>> -
>>   static void rm_map_entry_at(int idx)
>>   {
>>   	int i;
>> @@ -532,6 +384,17 @@ void mtrr_overwrite_state(struct mtrr_var_range *var,
>> unsigned int num_var,
>>   	mtrr_state_set = 1;
>>   }
>>
>> +static u8 type_merge(u8 type, u8 new_type, u8 *uniform)
>> +{
>> +	u8 effective_type;
>> +
>> +	effective_type = get_effective_type(type, new_type);
>> +	if (type != MTRR_TYPE_INVALID && type != effective_type)
>> +		*uniform = 0;
>> +
>> +	return effective_type;
>> +}
>> +
>>   /**
>>    * mtrr_type_lookup - look up memory type in MTRR
>>    *
>> @@ -540,66 +403,36 @@ void mtrr_overwrite_state(struct mtrr_var_range *var,
> 
> This last chunk of this patch is not applying correctly for me.  'patch' complains
> about a malformed patch.  I manually edited the changes in so I could build and
> test, but I'm unsure if something might be missing.

Weird. I changed a typo in the patch file itself, maybe I did some other
modification without noticing it. Will resend.

> 
>> unsigned int num_var,
>>    * MTRR_TYPE_INVALID - MTRR is disabled
>>    *
>>    * Output Argument:
>> - * uniform - Set to 1 when an MTRR covers the region uniformly, i.e. the
>> - *	     region is fully covered by a single MTRR entry or the default
>> - *	     type.
>> + * uniform - Set to 1 when the returned MTRR type is valid for the whole
>> + *	     region, set to 0 else.
>>    */
>>   u8 mtrr_type_lookup(u64 start, u64 end, u8 *uniform)
>>   {
>> -	u8 type, prev_type, is_uniform = 1, dummy;
>> -	int repeat;
>> -	u64 partial_end;
>> -
>> -	/* Make end inclusive instead of exclusive */
>> -	end--;
>> +	u8 type = MTRR_TYPE_INVALID;
>> +	unsigned int i;
>>
>> -	if (!mtrr_state_set)
>> +	if (!mtrr_state_set || !cache_map) {
>> +		*uniform = 0;	/* Uniformity is unknown. */
>>   		return MTRR_TYPE_INVALID;
>> +	}
>> +
>> +	*uniform = 1;
>>
>>   	if (!(mtrr_state.enabled & MTRR_STATE_MTRR_ENABLED))
>>   		return MTRR_TYPE_INVALID;
>>
>> -	/*
>> -	 * Look up the fixed ranges first, which take priority over
>> -	 * the variable ranges.
>> -	 */
>> -	if ((start < 0x100000) &&
>> -	    (mtrr_state.have_fixed) &&
>> -	    (mtrr_state.enabled & MTRR_STATE_MTRR_FIXED_ENABLED)) {
>> -		is_uniform = 0;
>> -		type = mtrr_type_lookup_fixed(start, end);
>> -		goto out;
>> -	}
>> -
>> -	/*
>> -	 * Look up the variable ranges.  Look of multiple ranges matching
>> -	 * this address and pick type as per MTRR precedence.
>> -	 */
>> -	type = mtrr_type_lookup_variable(start, end, &partial_end,
>> -					 &repeat, &is_uniform);
>> +	for (i = 0; i < cache_map_n && start < end; i++) {
>> +		if (start >= cache_map[i].end)
>> +			continue;
>> +		if (start < cache_map[i].start)
>> +			type = type_merge(type, mtrr_state.def_type, uniform);
>> +		type = type_merge(type, cache_map[i].type, uniform);
> 
> This determination of the type isn't working for me in a normal VM (*not*
> SEV-SNP) that has MTRRs and produces a reasonable cache_map.  The
> cache_map contents are this:
> 
> [    0.027214] mtrr map 0: start 0 end a0000 type 6 fixed 1
> [    0.033710] mtrr map 1: start a0000 end 100000 type 0 fixed 1
> [    0.040958] mtrr map 2: start 100000 end 1100000000 type 6 fixed 0
> 
> The lookup is done for start = f7ff8000 and end = f7ff9000.   cache_map
> entries 0 and 1 take the "continue" path as expected.  cache_map entry
> 2 matches, so type_merge is called with type = MTRR_TYPE_INVALID and
> cache_map[i].type is 6 (MTRR_TYPE_WRITEBACK).   But type_merge()
> returns MTRR_TYPE_UNCACHABLE because get_effective_type() finds
> type1 != type2.
> 
> I don't fully have my head wrapped around your new code, so I'm just
> pointing out the problem, not the solution. :-(   Or maybe this problem
> is due to the patch itself being malformed as mentioned above.

Oh, what a silly bug. Thanks for the analysis!


Juergen

Download attachment "OpenPGP_0xB0DE9DD628BF132F.asc" of type "application/pgp-keys" (3099 bytes)

Download attachment "OpenPGP_signature" of type "application/pgp-signature" (496 bytes)

Powered by blists - more mailing lists